Charger options for 12v bp5 battery

Hi, Can someone advise on different ways to recharge this battery Outside project. I have 3 of these batteries. Do I just charge with standard car battery charger? What should I look out for please? I need to charge all three and take to event.can then charge them at home for future use. Can I use a PC power supply to charge them?

My project needs to power an UNO , 7 digit 7seg display with 8v forward current req for each seg. 20plus LEDs at various times . The 7 seg and uno will be on for 5 hrs or so. The 20 LEDs on for seconds at a time then off.


I would call them lead-acid gel batteries, but the documents says VRLA batteries. I think that is the same.

These types of batteries are the easiest to charge but also the most dangerous when charged improperly.

Firstly I recommend you use a charger designed for that type of battery.

Similar to what the link said, most of the charge is with constant current, then at the end you use a constant voltage. Unless you have some means of monitoring the current and voltage and have a program to modify them, you probably should’t be doing it.

These are very simple batteries to charge in principle, they stop taking current when they are fully charged all on there own. You could just apply its rated voltage to the terminals and it would charge up, but the problem is that they will overheat if you try to charge them to fast. Which is why you should limit the current to about 10-20% of its rated Amp/Hours and never ever more then 100% unless otherwise stated in its spec sheet. Also when you reach its max charge if you don’t disconnect the voltage it will start doing micro charge/discharge cycles putting strain on the cells, although from what I understand not much of a issue on lead acid, but a very big issue on lithium batteries.

Again not really any information for you to charge them, get a proper charger, so much easier and safer.

many thanks for the replies. I'm all for safety first before cost. looking to buy one of these:

I trust this will safely charge the batteries?

just so I can learn a little from this though...

1) what does "5.0Ah @ 20 hour rate F.V.(1.75V/cell)" actually mean? im fine with understanding the 5 Ah's - this means it will provide 12 v at 5amps for 1hr, or 12v at 1amp for 5 hrs.

just confused ref the 20 hour rate and the F.V....

also ,

2) the max charge current says 1.5amps. i assume if i buy the above charger (4amps max), it will just draw the current it requires, and then top itself up - as per the links provided above.


I have one of those, and my charger is inside just a transformer with a few diodes and an current meter (a few windings of wire and a pointer).
So the 4A is not very accurate and the (top) voltage is not very accurate. The top voltage might be too high for such a small battery.

Note the maximum charge current of 1.5A.

One simple way to charge is to charge to constant voltage (13.5V or so) with a current limiting circuit to prevent current exceeding 1.5A (for instance a bench power supply can be set to do this).

The manufacturer probably has some application notes about preferred charging schemes, but checkout what says about AGM SLA's

Whatever you do DONT use a car battery charger, you'll burst this battery that way.

going to order this…

snip the plug off and attach battery clips. ill test using my multimeter regularly but from reading the links that have been posted im looking at 10hrs to get a full charge if completely depleted battery. Ive read somewhere about sticking a diode on the positive lead… is this necessary with a regulated power pack?

Im just starting out in arduino/electronics and need a battery charging solution for these batteries quite quickly. hopefully in years to come i will laugh at the £20 i spent on a regulated power supply - when i could have made one for pennies using old pc parts!

thanks for all the help.

liddlec7: 1) what does "5.0Ah @ 20 hour rate F.V.(1.75V/cell)" actually mean? im fine with understanding the 5 Ah's - this means it will provide 12 v at 5amps for 1hr, or 12v at 1amp for 5 hrs.

"5.0Ah @ 20 hour rate" means that if you discharge it over a period of 20 hours then you will be able to get a full 5Ah from it. Batteries exhibit less total capacity when you discharge them more quickly. Saying "12v at 5A for 1hr or 12V at 1A for 5 hrs", in practice, isn't correct. If you discharged it at 5A it might only last 30 minutes.

I'm not sure what "F.V." means. 1.75V/cell would be the minimum voltage for the battery before you start doing damage to it (1.75V * 6 cells = 10.5V) so I assume they're referring to a safe discharge limit.