When to replace battery

[billvolz]

My set up. I have 12VDC telemetry on top of a water tank with battery and solar for power. The batteries are two 6V lead acid AGM 110 AH deep cycle golf cart batteries in series. The solar panel is a single 330 watt and I'm using a Victron 100/20 charge controller to mediate power. The telemetry uses about 180 watts/day. The design was to have 7 days of power without sun and assumed a 50% discharge.

At some point the batteries will need to be replaced. How will I know when? Obviously when it fails to run over night would be a major clue. But I'd like to replace them before they get to that point.

The Victron gives me history info that includes time in bulk, absorption and float charging, solar panel yield and load consumption. Not a lot of info. Would a battery monitor provide the info? Victron has one but I don't want to spend $200+.

Thanks,

[SunEagle]

It really depends on what the battery manufacturer provides in cycle counts and DOD%. There really is no way to measure the health of an AGM sealed battery. But if those have a way to measure the specific gravity you will get a better idea of their life.

It is almost like a water heater. I know very few people that will change one out before it starts leaking but if your loads are critical I would replace the batteries at about 1/2 their life expectancy again based on the estimated number of cycles and the battery manufacturer data.

[chrisski]

I spent the $200+ For the Victron BMV 712, and it does not remember historical date. It remembers Record highs and # of alarms, but you can’t go back 2 days to find out what happened, never mind years. I don’t think that’s what you’re looking for.

THe smart shunt gives the same data I mentioned for closer to $100, but you can search wireless shunt on amazon and come up with cheaper options.

Victron has another piece of equipment that is supposed to log data, I think its called the Cerbex, but whatever it is, the documentation is not there to tell me exactly what it displays. I think it is closer to $200.