My aunt has a mobility scooter which seems to go through batteries too quickly. Recently, in addition to replacing the batteries, I also bought a new charger. The old charger was rated as 24V, 2A. Replacement chargers on Amazon were so inexpensive (~$12) that I was concerned about their quality, so I got a more heavy duty charger rated at 3 amps instead of 2. If I understand correctly, this is OK and may charge the batteries more quickly.
The charger charges very well, except most times it never goes into float mode and just keeps on going on at full charge (according to LED indicators). Most of the time during charging the charger gets only a bit warm and the battery case stays cool. At some point (I assume when the batteries are fully charged), the charger gets very warm and the battery pack holding the two batteries becomes quit warm also.
Is the use of a 3 amp charger a problem? Is the heat generated by the batteries indicative of overcharging? Any advice is appreciated.
I don’t know what type of battery is used. It’s important insofar as the exact charging rate or algorithm. In general, current is drawn by the battery, not applied so it’s a matter of providing as much current as the battery will accept within a certain percentage of the total ampere hour capacity, say 20%. It sounds more complicated than it is. The charger should therefore be “sized” to efficiently and safely charge the battery within a reasonable amount of time. The beauty of batteries (or Achilles heel) is that despite some improvements, the science was hashed out a hundred years ago.
A good quality battery of the proper type should give good service if it is charged properly and completely. An AGM or “deep cycle” battery is designed to be discharged and recharged from near dead conditions, I would assume that is what we are talking about? Maybe more modern lithium ion batteries are used today, I don’t know. But an automotive start battery would be quickly ruined in this kind of application, they are not designed for deep discharges.
These are 12 volt batteries? Maybe similar to a motorcycle battery in terms of Ah capacity? I would make sure they are charged thoroughly before being put into service, and that the correct charger is mated with the type of battery. It is better to buy cheap batteries and a good charger than the other way around. It sounds like the chargers are choking, for whatever reason. Hook an accurate voltmeter that reads out to at least two significant digits and watch as it charges. You can bounce those voltages off the charts in the link above. They should match closely. It may take several hours - 8 to 12 easy, to bring them up to charge. A “12 volt” battery is really closer to 13 when charged, and takes closer to 15 to reach a full charge. You don’t want hot batteries, mostly. Bad. Here’s another link, hope this helps.
Do you mean that newly charged batteries run down after less distance than you expect? IOW, she expects to be able to scoot for two miles on a single charge, but instead she finds that the batteries run down after not even one mile.
Or do you mean that newly purchased batteries become unable to hold a complete charge after too few charging cycles? IOW, she expects a new set of batteries to still be giving full mileage per charge after a year of use, but instead she finds that after just 3 months the new batteries are giving much less than full mileage per charge.
These are two very different problems with two very different solutions.
Knowing the details of battery make and model and capacity would also be helpful. As well as the brand and model of scooter so we can confirm that the batteries she has are even the correct ones for the scooter she has.
Sounds like the charger is over-charging the batteries. A decent lead-acid charger will charge the battery in three stages: a constant current charge, maintained until a set voltage is reached, then a topping charge that maintains that voltage with a current that decreases over time, then a float charge at a slightly lower voltage and low current.
The float charge voltage is critical (about 2.25 to 2.27 V per cell at room temperature); much lower and the battery won’t be fully charged, much higher and the battery will be damaged. To make life more complicated there’s a temperature coefficient on the float charge voltage to account for.
Are the batteries removed and charged? Or charged while in the scooter?
If they remain in the scooter, there may be an electrical fault that has the charging current leaking into other parts of the scooter electronics. The fault may also be draining the batteries faster when in service.
Yes, two 12 volt batteries in series for 24 volt output.
She mainly complains of trouble going up a hill and having to zig zag to make it up. She stays within the condo complex while walking her dogs so the distance is not very far, so the only stress are the hilly streets.
Over a year ago I got her 2 MK batteries (12 volt) with a higher amp/hour rating – something like 18 AH instead of 12 AH. I think MK batteries are quality batteries. The scooter is a Go-Go Elite Traveller. I’m sure the replacement batteries are proper for this scooter. Recently my aunt had her scooter guy replace the batteries; I don’t know the brand.
The batteries are charged while in the scooter.
There was an electrical modification by the scooter guy which I had to fix when the fuse started blowing, so it’s possible there is still a problem with that.
The good news is that I put the scooter on the charger when I started this thread, and after an hour or two the charger went into float mode as it should (there was a pretty good charge already.) So I think I’ll just keep an eye on it and see if the problem is resolved. Also, I’ve taken over the charging of the batteries so I think it will be fine now. (I think my aunt just wasn’t charging the batteries often enough.)
The life of the batteries will be shortened by constant partial charging. It is best to let them run down before charging. Reading the specs for that chair I see that it is good for a 14% slope. I would assume this is for a light rider and fully charged batteries.
I’m wondering if she simply does not have an appropriate scooter for the conditions; you did mention hilly streets. That scooter looks to me like it is basically an indoor scooter (I am not trying to say she shouldn’t use it outside at all; just that it looks awfully light weight).
Now, I use my scooter outdoors in Edmonton winters, so my needs are probably radically different from hers, but I don’t even consider mine a fully outdoor one. It is considered “indoor/outdoor”. It is a Shoprider 778 Cobra, and takes two 35AH batteries; substantially heavier-duty than hers. I’ve been tempted to get an even heavier duty one but am concerned about using a really heavy duty scooter indoors.
Yes, I’ve heard that the number of charging cycles has a major impact on battery life. On the other hand, I don’t think SLA (sealed lead acid) batteries are designed for deep discharge, so I’m taking a middle ground and only charging when the battery gauge shows some significant reduction in the gauge reading under full power.
Some SLA batteries are designed for deep discharge. The Optima series of batteries have both deep cycle and non-deep cycle versions. That’s not to say that your particular battery is designed for that service.