# How to Choose a Lead Acid Battery Charger?

It has been suggested that you can charge sealed lead acid batteries with a normal power supply.

On the other hand, chargers are available for purchase, but cost almost $100. Is there a reason to go with the store bought battery charger? If so, I have six 6V lead acid batteries that I need to charge. The maximum allowed charge current is 1.5A. Many chargers (unlike the one I linked above) only put 2A or more. Is there a way to make that sort of charger easily work? And do I really need to spend almost$600 on chargers if I want to be able to charge all of my batteries at once? Or can I hook them up in parallel. I have been reading pretty extensively on this over the last couple of days, but am finding conflicting information everywhere. The Battery University source seems good, but it also isn't immediately clear to me what to purchase. I don't want to screw up and end up buying an expensive charger that doesn't work, but I also don't want to spend days figuring out how these work, when this is just a small component of an experiment that I need to have working ASAP. (Therefore, I will go with whatever is easiest!)

• There is plenty of information on the internet about how to charge lead acid batteries. 6x lead acid batteries in series might need a 40V battery to charge them and this is probably more economical than buying 6 chargers. Jun 29, 2016 at 17:13
• I don't know if I would try to charge the batteries in series or parallel, especially if they have different charge levels. I use a "standard" lab bench supply, but I only ever need to charge at most one at a time, and I use the supply for other things so the extra cost is well worth it for me. Jun 29, 2016 at 17:49

## 3 Answers

The Amp hour (Ah) rating of your batteries will make a difference on what size charger you should use to charge your cells. Any charger providing a current with a value of more than (Ah/4) is considered a fast charging unit for that battery. If you need your batteries to last, you should not use this method.

The method of parallel charging is acceptable, but will slow down the charge rate, essentially splitting your current by the number of batteries in parallel. This method, combined with the knowledge above could bring down the current from a 'fast charging' unit to an acceptable charging range.

The biggest problem with using a regular power supply to charge your batteries is that the charging will have to be very closely monitored. If the batteries become over-charged, electrolysis of the water in the cells will start to degrade the batteries. A battery charger will have the necessary circuitry to maintain a constant voltage, limiting the possibility of over-charging.

I've always thought that this model looked interesting: https://www.amazon.com/NOCO-G750-UltraSafe-Battery-Charger/dp/B004LX3AS6/ref=sr_1_4?ie=UTF8&qid=1467226159&sr=8-4&keywords=lead+acid+battery+charger

It has a big-brother version that can charge 4 at a time.

I'd be strongly disinclined to charge them either in series or in parallel. A better approach would have separate regulators for each connected battery, as does the unit I linked to.

The lead-acid charging is pretty simple, as these things go, and is readily accomplished with a lab power supply having both constant current and constant voltage (as they generally do), with just a little attention to when to switch from 14.4V accumulation charging to 13.7V float charging. I expect you've seen that already in the question you linked to.

I don't see how you'd accomplish that in series or in parallel. In series they all get the same current, which could overcharge one or more if they are out of balance. In parallel they all get the same voltage, which I suppose could possibly work OK if you used a conservative current limit, but that would lengthen charging time.

Anyway, I'm thinking one charging circuit per battery is most reliable. Whether or not these regulation circuits all feed off the same "bulk" supply internally would be a question of pricing and convenience (size and sprawl I expect :).

I like this page on lead-acid charging: http://www.evdl.org/pages/hartcharge.html

It's a little rambling in style but seems to hit all the important points well above the fold :)

A maximum charge rate of 1.5A suggests a small capacity battery (7.5Ah at 5 hour rate) which is probably an SLA (Sealed Lead Acid) type. SLA batteries should be charged slowly (10 hour rate or longer) and never allowed to reach gassing voltage.

Unlike flooded lead acid batteries (which can be balanced simply by overcharging and then topping up with distilled water) SLA batteries must be balanced by voltage alone. So if you want to charge a bank of several batteries in series then you should charge each one separately beforehand to make sure they all have the same voltage. You can then use a charger rated for the total voltage, but you should check the balance regularly and charge them separately again if needed.

If you intend to use the batteries separately then just get sufficient 6V SLA chargers to do as many as you need to at once. Low current SLA chargers are cheap enough that you should be able to afford one per battery. You could also use them to charge and balance the individual batteries in a series connected bank.

• Is it problematic to charge at the maximum rate? (1.5A) The batteries are 5Ah @ 20 hour rate. The poster above implies I shouldn't go past 1.25A, but that isn't so different from 1.5A, I guess. Jun 29, 2016 at 21:46
• A slightly higher current will probably shorten its lifespan a little (not as much as over-charging or over-discharging). However when charging at a higher rate the battery just reaches float voltage earlier and doesn't charge much faster, so why do it? If you can find a charger with lower current (eg. 0.5A) then use it. Jun 29, 2016 at 23:55