New to this with questions

MinnowLady · May 26

We have acquired a cabin in Ontario that is only used for 2-3 months of the year and has a solar system.

When we opened up last week (for the first time), the solar system appeared to be fine--i.e., things turned on. However, when I checked the batteries, which are flooded lead-acid, I found they were low on water. I couldn't tell if they were bone dry, but the liquid was certainly below the tops of the plates. Since that's bad for car batteries, I'm assuming it's bad for solar batteries.

We were told they were topped off in September last year before things were closed up. There was also some noticeable corrosion on the terminals. My not-educated guess is that they boiled a bit in the winter, resulting in the low water and the corrosion from the vapor depositing on the terminals.

Question #1: Is this a reasonable supposition?

Question #2: What can I do about it?

I don't want the batteries to freeze over the winter (-20°C), but at the same time, I don't want to destroy them by boiling.

If it matters, the system is 24V with 4 × 395W panels and 4 × 430 Ah 6V batteries. The charge controller is a MidNite Solar MN3024DIY.

SumPower · May 28

Question #1: Is this a reasonable supposition? Yes

Question #2: What can I do about it?

Lead acid batteries need to be checked for water level weekly, monthly at a minimum depending on the manufacturer.

If the water level has been below the plates for an extended period of time, they are likely dead. Look at the voltage difference of each battery. For example one might be 11 volts and another may be 8 volts. The 8 volt is likely dead. Just a comparative analysis.

Take a voltage reading of each battery and record it. If they are below 9.6 volts and have been at this voltage without water, then they are on the downhill slope.

Only way to find out is to add distilled water and charge them per the maufacturers voltage recommendations for each stage.

MinnowLady · May 28

Thank you. It sounds to me like this is the wrong battery technology for us.

SumPower · May 29

AGM batteries would be a better fit as the self discharge is low compared to Lead acid. Charge them up and disconnect them until spring.

Lithium would also work if you charge them before you leave for the winter and disconnect them until springs warmer weather.

littleharbor2 · May 29

It is not recommended to leave a bank of fully charged lithium battery is sitting idle for months at a time Bring up to 60% and then disconnect them

NANOcontrol · May 29

I leave lead acid batteries at my camp over winter for years and have not had an issue and these batteries are from town recycling! My charging system is only a couple amps. No mention of how old these batteries are. When you are gone there shouldn't be a lot of cycling and therefore no boiling away of water. There may be a dead cell causing excess charging. Something is wrong. Lead is a good choice for this application, lithium is not. Charging a lithium battery below freezing will destroy it.

Wheelman55 · May 30

littleharbor2 said:

It is not recommended to leave a bank of fully charged lithium battery is sitting idle for months at a time Bring up to 60% and then disconnect them

For lithium you should check with the battery manufacturer.

For instance: Discover used to recommend 60% for storage. These days they recommend 100%.

NANOcontrol · May 30

Over winter in your norther location the panels could be covered for months. It might be a good idea to add an additional panel which is perfectly vertical so snow will not cover it. Even charge controllers present a load and can drain a battery when panels are covered for a long time. Loads can be a real battery killer when there is no monitoring to disconnect them in poor production periods.

New to this with questions

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