How much water should I add to old AGM battery?

[davethedrummer]

Have you considered the effect on the "flimsy little valve caps" of the plastic cover which you removed to expose them? When constrained from the top from simply popping off, I expect that the rubber caps could provide a very controlled pressure relief function.

Of course I considered that. I should have mentioned that a few of the caps on some batteries had popped off already when I opened the chassis. You can also see the green evidence of overflow on one of the pics I posted before. The surviving battery in question also popped a few caps while doing a prolonged charge. I think in their factory state there is no excess liquid in the cells and because they do not have to be re-filled during their lifecycle they can be called maintenance-free. However that does not mean they cannot overflow on a really hot day.

[sdold]

I think the two slots shown below function as the pressure relief valve by letting excess pressure escape past the sides of the cap, even with the cap held tightly by the cover. I bet they would pop off with even less pressure than that if the top was removed.

VRLA valve.jpg

[inetdog]

Of course I considered that. I should have mentioned that a few of the caps on some batteries had popped off already when I opened the chassis. You can also see the green evidence of overflow on one of the pics I posted before. The surviving battery in question also popped a few caps while doing a prolonged charge. I think in their factory state there is no excess liquid in the cells and because they do not have to be re-filled during their lifecycle they can be called maintenance-free. However that does not mean they cannot overflow on a really hot day.

To me that indicates that the batteries have, at some point, been seriously overcharged. Under normal charging conditions (which may be substantially lower current as a function of capacity, C, for these telecom float batteries than for more typical AGMs intended for cycle service) any oxygen and hydrogen gas produced will be recombined without venting. If electrolyte is actually lost in the process, rather than just gases, I suspect that either the boil-off was particularly violent or the cells were inverted at the time (strongly not recommended!)
AGM batteries should NOT ever be subject to a high current/high voltage charging regime such as that recommended for equalization in a flooded (FLA) battery.

[GeorgeF]

One more question about the so called telecom thin plate pure led batteries like NS Red. According to specs able to 400 cycles DoD 50%. If during 5 years of service cycled lets say only 50 times can you still expect few hundred cycles after service?

[inetdog]

One more question about the so called telecom thin plate pure led batteries like NS Red. According to specs able to 400 cycles DoD 50%. If during 5 years of service cycled lets say only 50 times can you still expect few hundred cycles after service?

Yes and No. Both discharge/recharge cycles and calendar time reduce the capacity and life of the battery. If the warranty is 5 years or 400 cycles, you may have little left (of the typical 809% of original capacity at End Of Life) after 5 years, regardless of the number of cycles. If the warranty is 10 years, then yes, you probably have 200+ cycles left.

[GeorgeF]

I see this on their website. 400cycles 80%DoD. For a thin plate battery it is not bad. If I understand well the warranty period is 4 years