Determining AH rating of aging batteries
My Trojan 125's are almost 5 years old now, when they were new they were rated at 240 Ah. Now my trimetric is showing 70% at 12.1 volts which I know is wrong. So how can I determine the true Ah rati...
Forum Discussion
BFL13 wrote:
Run the ten hour test at the 20AH rate to see how long it takes to get to 50% (50% measured by SG and confirmed by voltage after waiting an hour after removing the load)
240AH 20 hr rate is 12 amps ( four 3 amp lamps or whatever) Use the Trimetric AH counter for more confirmation.
Say it takes 9 hrs to get down to Trojan's 50% SG of 1.172 and after an hour of bounce back you are nearing 12.1v so you are at about 50%
9 out of 10 is 90% or 216AH of 240 (Trimetric AH count for comparison cross-check)
If you use lamps then they dim as voltage drops and your 12 amps gets less so turn on more lamps as test goes on. If you use an inverter and some load to get 12a then you get inverter creep up in amps as voltage drops so in that case start with 11 and end with 13 to get 12 average.
If you are lower in capacity then try a serious session of overcharging at 15.5v to see if you can get the SG up if some of the sulfation is not yet permanent.
Without reading this post first, I ran a 12 amp load for 10 hours, the voltage was down to 11.9 on my trimetric, but after reading your post I shoulda let them 'come up' for an hour after my test?
Guess I gotta run it again..?
