A battery can lose – depending on how and where it is stored – up to 30% of its charge per month – just sitting around the house or garage! And there are all kinds of things that affect battery charge and loss thereof (like temperature, humidity, state of discharge, age of battery, etc). Most of us never consider any of them.
Whether or not your boat is stored for the season in a warm garage or out in the cold, your best bet is to remove all batteries and bring them inside. A fully charged battery with a perfect electrolyte level can probably withstand temperatures down to zero degrees without freezing. But the colder it gets, the more easily a battery can discharge, and therefore the more easily it can then freeze at higher temps. If even one of the cells freezes, the battery is shot!
Fully charge them about once a month over the winter and they will be ready when you are in the spring. Try to keep them off of concrete floors if possible and cover the terminals to help prevent discharge. The last thing you want is a dead battery on the launch ramp on opening day, or a dead trolling motor battery.
No matter what kind of battery chemistry you choose, follow these recommendations to get the best performance and longest life from your batteries:
- Stay with one battery chemistry (flooded, gel or AGM). Each battery type requires specific charging voltages and currents. Mixing battery types can result in under- or over-charging, which may mean replacing all batteries on board at the same time.
- Never mix old batteries with new ones in the same bank. Old batteries tend to pull down the new ones to their deteriorated level.
- Regulate charge voltages based on battery temperature and acceptance (either manually or with smart-sensing devices) to maximize battery life and reduce charge time. Ensure that your charging system is capable of delivering sufficient amperage to charge the battery banks efficiently.
- Keep batteries clean, cool and dry.
- Check terminal connectors regularly to avoid loss of conductivity.
- Check fluid levels and add distilled water to flooded lead acid batteries when needed. Keep batteries charged; leaving them in a discharged state for any length of time will damage them and lower their capacity; it also reduces lifetime.
- Clean corrosion with a paste of baking soda and water.