# Electrical guys - slow battery charger **URL:** \ **Category:** Factual Questions\ **Created:** [November 6, 2012, 10:06am UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059 "2012-11-06T10:06:21Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Busy\_Scissors](https://avatars.discourse-cdn.com/v4/letter/b/d78d45/32.png) [@Busy\_Scissors](https://boards.straightdope.com/u/Busy_Scissors)\ **Post date:** [November 6, 2012, 10:06am UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059/1 "2012-11-06T10:06:21Z")
I use torches for night riding with rechargeable batteries, and they seem to take forever to charge. Could someone tell me if this is normal - the specs are: Two 3.7V lithium batteries (brand trustfire), 2.5 A, TR18650 take around 12 hours to charge. The charger is a model WF-139 with listed inputs as input1 100-240V, input2 12V - 400mA, output 4.2V - 450mA. Given the torch lasts about an hour on full setting, it’s always struck me as a long time to charge. Maybe it’s normal though? ---
**Author:** ![Indiana](https://avatars.discourse-cdn.com/v4/letter/i/8edcca/32.png) [@Indiana](https://boards.straightdope.com/u/Indiana)\ **Post date:** [November 6, 2012, 2:17pm UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059/2 "2012-11-06T14:17:28Z")
Busy, Your charge time looks normal. Here’s how it works: Battery **capacity** is given in mAh (milli amp hours). Your batteries are 2.5 Ah (amp hours) or 2500 **milli** amp hours. Your charger’s output is 450 mA (milli amps). From here out, it is simple math. For 2 2500mAh batteries: (2\*2500mAh)/450 mA = 11.1 hours charge time if they are mostly discharged. Given some inefficiency in the process, close to 12 hours seems reasonable. ---
**Author:** ![Indiana](https://avatars.discourse-cdn.com/v4/letter/i/8edcca/32.png) [@Indiana](https://boards.straightdope.com/u/Indiana)\ **Post date:** [November 6, 2012, 2:38pm UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059/3 "2012-11-06T14:38:01Z")
More info: The “A” in mAh is Amperes a.k.a. Amps, a measure of the rate at which electricity is being delivered to your lamp. In this case, your batteries have the ability to deliver 5000 milli Amps for 1 hour, but your charger can only replenish them at a rate of 450 milli Amps an hour. Your ability to discharge, is more than 10 times your ability to charge. The fact that you have a 5000mAh battery and your batteries last for one hour is kind of a coincedence. It means your lamp is using 5000mA. If you had a different lamp that used 2500mA, your batteries would last twice as long. Or conversely, if your lamp used 10000mA, your batteries would last half as long. ---
**Author:** ![Busy\_Scissors](https://avatars.discourse-cdn.com/v4/letter/b/d78d45/32.png) [@Busy\_Scissors](https://boards.straightdope.com/u/Busy_Scissors)\ **Post date:** [November 6, 2012, 3:54pm UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059/4 "2012-11-06T15:54:35Z")
Ty Indiana, v clear. I guess I need to get a higher rated charger then to hurry things along. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [November 7, 2012, 12:22am UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059/5 "2012-11-07T00:22:26Z")
I have one of these: [DealExtreme SKU 6105](http://dx.com/p/digital-li-ion-18650-battery-charger-6105?item=1) Note that it is sold out. Sorry, visual aid only. It lists the charge current at one amp so that would cut your time in half. I’ve never notice how long it takes to charge my 18650’s (Ultrafire 3000mAh, no doubt overrated) but 12 hours does seem excessive, though realistic for your charge current. If I had to replace it, I’d go with this one: [DealX SKU 163044](http://dx.com/p/trustfire-tr-006-dual-slot-25500-26650-26700-18650-16340-battery-charger-ac-110-240v-163044?item=7) Multi voltage, 1amp out, 100-240vac in, adjustable trays for a number of batt sizes. Trustfire branding is a plus IMO. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [November 7, 2012, 4:52pm UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059/6 "2012-11-07T16:52:55Z")
Another factor is the charging protocol. Charging protocols can vary dramatically and can have a big impact on charge times and batter life. The simplest protocols are “just charge, until voltage is X”. Better ones drain the battery first, then charge, and charge at different voltages depending on the battery’s voltage. Google it and you’ll find it’s not nearly as simple as you’d think. Sometimes chargers that take longer are helping give your batteries a longer lifespan. Of course, you can’t charge any faster than the charger’s output allows, so this isn’t an argument against getting a heftier charger. ---
**Author:** ![LisbyOrtizd](https://avatars.discourse-cdn.com/v4/letter/l/e480ec/32.png) [@LisbyOrtizd](https://boards.straightdope.com/u/LisbyOrtizd)\ **Post date:** [August 31, 2013, 4:30pm UTC](https://boards.straightdope.com/t/electrical-guys-slow-battery-charger/640059/7 "2013-08-31T16:30:06Z")
The charging time is normal, though it should take a little less time, but that is an other thing if you have a faulty charger. I bought some [deep cycle batteries](http://www.mrpositive.co.nz/deep-cycle-lead-acid-batteries) and they take long time to charge, but people say that it is normal. I guess its just the way it works, as described by **Indiana** above.