# Battery charger rated amperages **URL:** \ **Category:** Factual Questions\ **Created:** [June 18, 2014, 12:11am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022 "2014-06-18T00:11:01Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [June 18, 2014, 12:11am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/1 "2014-06-18T00:11:01Z")
I am paraplegic and use an electric scooter (as well as a manual wheelchair, but that is irrelevant to the question). As is normal with such things it uses 2 gel-cell batteries (lead-acid, but with the acid in a spill-proof gell), so it uses a charger that puts out 24 volts. I still have the charger for my previous scooter. That charger is rated at 5 Amps output. The charger for my current scooter is rated at 3 Amps output. Given that the voltage is the same, does it matter if I use the old charger on my current scooter (the connections are the same)? Since both are automatic chargers I fail to see how that would make a difference to the batteries. The one that came with my current scooter is fine; I just like the old one better because it is less of a pain plugging in to the wall (it has a power switch that the current one doesn’t, so I can leave the old one plugged in to the wall and use the power switch to turn it on and off). ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [June 18, 2014, 1:52am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/2 "2014-06-18T01:52:03Z")
I’m going to go with ‘probably…’ Generally speaking, the device will draw the current it wants, up to the max of the charger. Since you want to use a more powerful charger than the chair needs, that shouldn’t be an issue. If you were talking about cell phones, I’d say you’re in the clear to use the old charger. BUT…you need to make sure that all the charging intelligence is in the chair, not the charger. It probably is in the chair…but if not, you could be applying the wrong algorithm. That can cause anything from no charge, to weakening the battery over time, to (less likely) explosions. Do the chargers have model numbers or anything that we could look up to verify the details? ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [June 18, 2014, 3:11am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/3 "2014-06-18T03:11:26Z")
I believe you will be okay with a larger charger. What is this algorithm of which the previous poster speaks? I would think it is just voltage regulation. ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [June 18, 2014, 3:54am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/4 "2014-06-18T03:54:31Z")
> [@carnivorousplant](#): > > I believe you will be okay with a larger charger. > What is this algorithm of which the previous poster speaks? I would think it is just voltage regulation. You can charge a battery just by putting a higher voltage on it. But if you control the current, you can tune the charging for speed or battery life. If you push some kinds of batteries hard when charging, you can shorten their life. Also, some battery chemistry types are OK with being trickle charged at the top…some prefer to have the charge current turned off until they run down a bit, then charged again. I’d expect the chair to have a charging circuit that manages this, but it could be done from the charger in some scenarios. Another possible, but not very likely concern, is protection circuits. Back when I did power for cell phones, we had layers of safety. The battery would shut itself down if charged in a dangerous manner. The phone would do the same, if it detected a problem. And if the charger itself noticed an issue, it would turn off. It’s theoretically possible that the chair is relying on the charger for safety, and that the old charger doesn’t provide the same mechanism. Not likely in this case…but possible. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 18, 2014, 4:08am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/5 "2014-06-18T04:08:41Z")
The 5A charger may be putting out more voltage than the 3A charger, which could possibly damage the charge circuitry. Simple (unregulated) power supplies are rated for x Volts _at_ y amps. If your old charger was rated as 24v _at_ 5A, it might be putting out 30v at 3A. It’s probably not going to hurt anything, but it’s a possibility. ---
**Author:** ![Kansas\_Beekeeper](https://avatars.discourse-cdn.com/v4/letter/k/c37758/32.png) [@Kansas\_Beekeeper](https://boards.straightdope.com/u/Kansas_Beekeeper)\ **Post date:** [June 18, 2014, 4:09am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/6 "2014-06-18T04:09:39Z")
I’m not an electrical engineer or anything close to it. My comments are based on my experiences charging batteries on old tractors and trucks over many years. If the charger is automatic–if it tapers the current as it approaches charged-- a 3 amp vs. 5 amp will not matter except that the 5 amp might charge it a little faster, with no harm given the size batteries you are talking about. If they were old school manual chargers (and there was no charging circuit on the chair that regulates it), then the 5 amp would overcharge and boil the battery sooner than the 3 amp. ---
**Author:** ![bluezooky](https://avatars.discourse-cdn.com/v4/letter/b/e8c25b/32.png) [@bluezooky](https://boards.straightdope.com/u/bluezooky)\ **Post date:** [June 18, 2014, 7:18am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/7 "2014-06-18T07:18:16Z")
Bit hard to answer the question without knowing the amp hour rating of the batteries, if you have 12v 12 ah then the 3 amp charger would be ideal, having said that you should would get away with using the larger charger without any problems. ---
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [June 18, 2014, 1:46pm UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/8 "2014-06-18T13:46:18Z")
> [@bluezooky](#): > > Bit hard to answer the question without knowing the amp hour rating of the batteries, if you have 12v 12 ah then the 3 amp charger would be ideal, having said that you should would get away with using the larger charger without any problems. It would appear from looking at the specs (I can’t practically speaking get at the batteries to examine them myself) that I have 2 U1, 12v, 35ah batteries. ---
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [June 18, 2014, 1:50pm UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/9 "2014-06-18T13:50:02Z")
From looking at the comments I guess I’ll behave myself and continue to use the charger that came with my current scooter even though plugging and unplugging it from the wall is a p.i.t.a. Thanks. ---
**Author:** ![Matt1075](https://avatars.discourse-cdn.com/v4/letter/m/94ad74/32.png) [@Matt1075](https://boards.straightdope.com/u/Matt1075)\ **Post date:** [June 19, 2014, 5:05am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/10 "2014-06-19T05:05:23Z")
Canadjun, I have a couple of different gel-cell batteries I keep around for daily or emergency use. My experience with these batteries has taught me that 3 and 5 amp charge rates for the capacity you have is “very slow” and “slow”. I have a 12 volt 10AH battery that sees frequent use and gets charged at 6 amps with no apparent problems. I think you could easily use either charger with very little risk of any problems. Both chargers are designed to charge scooter batteries. The small difference in charge rate is insignificant. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [June 19, 2014, 5:57am UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/11 "2014-06-19T05:57:39Z")
> [@beowulff](#): > > The 5A charger may be putting out more voltage than the 3A charger, which could possibly damage the charge circuitry. > > Simple (unregulated) power supplies are rated for x Volts _at_ y amps. If your old charger was rated as 24v _at_ 5A, it might be putting out 30v at 3A. > > It’s probably not going to hurt anything, but it’s a possibility. Whaaaat? Can you explain this please, it makes no sense to me > [@Canadjun](#): > > It would appear from looking at the specs (I can’t practically speaking get at the batteries to examine them myself) that I have 2 U1, 12v, 35ah batteries. Are you sure they are both 24V chargers? (or for that matter are either of them 24V?) There are two ways to connect two 12V batteries together series and parallel. Series will give you 24V @35 Amp Hours. Good for high speed, but will drain the batteries quickly In parallel, you will have 12V @ 70Amp Hours, about what a car battery has. Longer life, better acceleration from a stop, lower top speed. If I had to guess, I would say they put the two batteries in parallel, but I’m not there looking at the wiring of your chair. If it is a 24V system, the batteries will like the 3A charger better (less chance for overheating). If it is a 12V system, either charger will be fine. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 19, 2014, 4:15pm UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/12 "2014-06-19T16:15:37Z")
> [@Rick](#): > > Whaaaat? Can you explain this please, it makes no sense to me Simple power supplies (transformer/rectifier/capacitor) are unregulated, and have significant voltage drop under load. In order to meet the rated spec of X volts _at_ Y amps, the voltage droop needs to be taken into account, which means the “unloaded” voltage can be significantly higher. I once ruined a gadget this way, by plugging in a much higher current adapter, even though the rated voltage was the same. ---
**Author:** ![Canadjun](https://avatars.discourse-cdn.com/v4/letter/c/76d3ee/32.png) [@Canadjun](https://boards.straightdope.com/u/Canadjun)\ **Post date:** [June 19, 2014, 4:17pm UTC](https://boards.straightdope.com/t/battery-charger-rated-amperages/691022/13 "2014-06-19T16:17:41Z")
> [@Rick](#): > > Whaaaat? Can you explain this please, it makes no sense to me > > Are you sure they are both 24V chargers? (or for that matter are either of them 24V?) > There are two ways to connect two 12V batteries together series and parallel. > Series will give you 24V @35 Amp Hours. Good for high speed, but will drain the batteries quickly > In parallel, you will have 12V @ 70Amp Hours, about what a car battery has. Longer life, better acceleration from a stop, lower top speed. > If I had to guess, I would say they put the two batteries in parallel, but I’m not there looking at the wiring of your chair. > If it is a 24V system, the batteries will like the 3A charger better (less chance for overheating). If it is a 12V system, either charger will be fine. Yes, they are **24v** chargers. Every electric scooter I have so far had (this is my 4th) has had 2 12V batteries charged with a 24V charger (presumably that means that the batteries are in series). I think typical electric wheelchairs are the same (although never having needed an electric wheelchair I know less about them). I can assure you the voltage and amperage output specs are on the chargers.