Battery problem?

[billvolz]

I have two identical telemetry systems on top of water tanks. The telemetry consumes about 180 watts/day. It's powered by solar/battery. I want the system to have enough power to run for 7 days without sunlight. For that I'm using two 6V 225AH deep cycle SLA AGM batteries in series from vmaxtanks.com. There is a single 330 watt solar panel and power is mediated by a Victron 100/20 charge controller. The system was installed in Nov 2019. These batteries are in battery boxes but outside where temps can get into the single digits for short periods and below freezing temps in the winter are common.

Besides other things, the telemetry monitors battery voltage and sends an email if it goes below 12.0 volts. I've started to get these emails from both systems. I thought the batteries would last for at least 5 years. Does this make sense that they would only last for 2 years? What would reduce their life? With a maximum discharge to 50% I have 1320 watts available and the telemetry uses about 90 watts overnight, or about 7%. So the battery is being maintained near 100% charge. The charge controller will stay in bulk charge for an average of 336 minutes which seems rather long for batteries that are discharged only 7%. When it switches to absorption it will spend an average if 142 minutes. And after that it will spend 315 in float with the bulk of that time during the summer.

The odd thing is that the change controller tells me the minimum battery voltage was 12.27 volts. Next time I'm over there I will check the voltage with my DMM and see if the charge controller and/or telemetry voltage is off.

The question is this. If I need to replace the batteries is there a better option? Lithium? LIPo? Cheapest ~220 AH batteries I can find? And do I perhaps have the wrong settings on the charge controller? I pretty much took the defaults for the SLA AGM batteries.

Thanks,

[SunEagle]

You really have to look at the number of posted cycles your battery system can provide at the discharge % they see. While you may have gotten more cycles out of the batteries I think the low temperatures or clouds may have cut the life span.

Depending on what that Victron CC can truly give you from the 330 watt panel also may be a factor in how well the batteries recharge. FLA type batteries would rather be in the C/8 to C/10 charge rate. They will work in the C/10 to C/12 area but may not last as long depending on how much they discharge.

[billvolz]

You really have to look at the number of posted cycles your battery system can provide at the discharge % they see. While you may have gotten more cycles out of the batteries I think the low temperatures or clouds may have cut the life span.

Depending on what that Victron CC can truly give you from the 330 watt panel also may be a factor in how well the batteries recharge. FLA type batteries would rather be in the C/8 to C/10 charge rate. They will work in the C/10 to C/12 area but may not last as long depending on how much they discharge.

If I'm reading the battery manufacture's graph right, at 10% DOD after 3600 cycles I should be around 60% of capacity. My DOD is actually closer to 4% so I should get a lot more cycles perhaps a bit more than double that - say 8000 cycles. I'll check the Victron to see if it tells me how many cycles it's done. Since the batteries were installed 2 years ago there should be about 700 cycles if one/day. If it's actually used 8000 cycles that would imply over 10 cycles/day. That might be true since it does spend an average of over 300 minutes in bulk charge. Low temps below freezing do occur but are not the norm. Typical winter temps are in the 40-50;s. Clouds might be an issue but nothing I can do about that. Another factor might be shading of the solar panel by trees. These tanks are in a clearing in woods with tall trees around and depending on the time of year and trees with/without leaves, might cause more cycles. Thanks