Thread: How do I check my battery's health?

G'day James,

Most places that install batteries will test yours for free and tell you the CCA of it and how desperately it needs replacing. It's also worth cleaning the terminals/clamps with sand paper and spraying them with some battery terminal protector to prevent oxidisation.

When you swapped the aux battery and the cranking battery did you get a new aux battery? If so you could use that to get you out of trouble.

If I was in your situation I would just make sure you have a decent set of jumper leads, usually people are willing to help out with a jump but particularly with the Defender it's good to have a set of extra long, extra heavy duty leads to get to the battery. I had mine made at a industrial supplies shop out of 35mm welding cable, does the trick nicely

if you have concerns and you are going on a big trip than i would change it out.........

at the price optimas are you probably what max. life out of it....but being able to start your car when nobody is around would be more important

Thanks guys.

Yes, md90, I did buy a new aux. I got a nice big Varta from rrturboD and put it in the larger spot where the OEM was (which had cracked). All I do if/when I need a jump is to connect the positive terminals and fire her up.

Weeds, you're probably right, but I'd not feel easy about it if I didn't test the battery myself so I knew for certain.

So, can anyone run me through how I do a proper test of the battery? I'm loathe to take it someone else, in part because by driving there I will have put a charge back into the battery so I'm guessing that it won't be a true test, and I can't afford to hand the thing over for a day or two.

Bump.

While waiting I've noticed another thread that's running where advice has been provided saying that the OP should charge his battery over a period of time and to then see how it goes (or something along those lines). He was also advised to then keep it up on a weekly/fortnightly basis. Is this all I can do? Just give it a hit with the charger and then hope it takes?

There must be a way for me to test things out a little more scientifically than simply going with "the vibe". I've got the gear (multimeter) but no idea, so a nudge in the right direction would be really appreciated.

Basic test worked for me mostly.

Engine not running check battery voltage (at posts) with multimeter 12.5 volts about.

Crank over engine, whilst checking battery voltage should maintain above 10 volts while cranking.

Much under 10volts spells bad battery generally.

Do the above test with known good battery to eliminate starter etc

Regards

Originally Posted by jc109

Bump.

While waiting I've noticed another thread that's running where advice has been provided saying that the OP should charge his battery over a period of time and to then see how it goes (or something along those lines). He was also advised to then keep it up on a weekly/fortnightly basis. Is this all I can do? Just give it a hit with the charger and then hope it takes?

There must be a way for me to test things out a little more scientifically than simply going with "the vibe". I've got the gear (multimeter) but no idea, so a nudge in the right direction would be really appreciated.

you need to do at least 5 measurements to acertain the health of your battery.

first put it on a charger and let it sit untill the charger says its charged if its smart OR if its a slow charger untill the charger has been on for long enough to completely charge the battery (battery Ah rate/chargers rated output *1.5)

remove the charger and let it sit, for at least 30 minutes.

it should now read between 12.8 and 13.2ish volts.

now put a load on it, you want about 20 amps which in most cars is high beam headlights + the heater fan on high at this point the volts shouldnt go below 12.5V and it should stay there for about 5 minutes minimum.

that ensures you got rid of any surface charge on the battery

now try to start the engine, the battery voltage shouldnt drop below 10.5V.

if you've cranked for less than 30 seconds to get a stable voltage while cranking the battery voltage should come right back to where it was.

let it sit for 24 hours and check the voltage again, it should still be right around 12.5.

if thats the case....

charge the battery again and then put a 25 amp load on it. leave it on untill the battery no longer holds 10.5 V under the 25A load.

The difference between that time and the Reserve capacity number on the battery is a rough approximation of the health of your battery expressed as a percentage.

Now these are rough and ready tests that I've used in the past and trust me, If you fail one of those tests with your battery you probably should have already replaced it if you're going to be relying on just that one battery.

battery terms really quick.

CCA how many amps the battery can push at ~-15 degrees for 30 seconds before the battery is depleted. This number is important for getting the engine to crank over, a high number here means the more likely you are to be able to get the engine to crank over fast enough to start.

RC how long in minutes the battery can push 25A at ~25 deg before the voltage under load drops below 10.5v This number is most important for running mid range loads, think small inverters and pumps.

Ah the total number of amps the battery has on offer, this is usually calculated at the 5 amp rate. (so divide this number by 5 and thats how long your battery will drive your engles compressor and an 11w fluro for in hours without recharging.) This number is most important for long low draws like engles, radios, led lights it also indicates how long it should take to charge the battery from flat. a small number here means the battery wont last long BUT it will also recharge quickly