We get a lot of customers asking us for guidance on solar battery maintenance and how best to use their deep cycle solar batteries to get the most life out of them. With the help of our battery manufacturer, Oliter, we’ve put together some answers to common questions to help you understand how a deep cycle battery works, what to avoid, and what you can do to protect your batteries. (Also known as Gel Lead Acid or VRLA batteries.)
What’s the difference between "cycle use" and "standby use"?
Cycle use - This is when the battery is used to power devices every day, which discharges the battery. The battery then must be recharged daily. The battery has a cycle of being charged and then discharged every day. This is the standard usage in an off-grid solar application.
Standby use – This is when for the majority of the time the battery remains 100% charged in standby. The only time it gets discharged is when there is there is no other power. This is common in uninterruptable power supplies. This is not how your batteries will be used in an off-grid solar application.
Standby use charge voltage at 25 °C: 13.5V-13.8V
Cycle use charge voltage at 25 °C: 14.1V-14.4V
What battery is best for solar usage?
A deep cycle battery should always be used in an off-grid solar application. This is because there are long periods of time where power is being drawn from the batteries, and when there is nothing to charge the battery. A deep cycle battery is designed to survive these prolonged, repeated, and deep discharges.
How are batteries rated?
Lead acid batteries are rated based on their capacity, which is measured by how much power a battery can put out in a given amount of time. For example, our 12V 200Ah battery is specified at C10, or 10 hours. This means that the battery can put out 200A in total over 10 hours, or 2400Wh.
How long can a battery last?
Our standard Gel VRLA batteries are designed to last about 5 years with proper care. We also supply lithium batteries which have an expected 10-15 year lifespan.
Do I need to add water as part of my solar battery maintenance?
No. Sealed lead acid and lithium batteries do not require additional water to maintain them.
What should I avoid when charging batteries?
- Avoid mixing batteries of different size and age – you will always be limited to the weakest battery in the string. For optimum performance, you should be using matched cells. Batteries should not be more than 6 months different in age.
- If the batteries are being charged in series e.g. at 48V, don’t run devices off just one battery to get 12V. Use a 48V to 12V step down. This ensures that the current is shared equally between the batteries, so that the they are all put under equal stress, and will all have the same lifespan.
- To get the best life out of your batteries avoid running more than 3 batteries/strings in parallel.
- Never go lower than 50% depth of discharge - not only will this permanently damage your battery and shorten the lifespan, but it will void your warranty.
- Never leave batteries partially charged. This will lead to sulfation and reduce your battery’s capacity, so always recharge to 100%.
- Don’t let your batteries get too cold or too hot – about 20°C is an ideal temperature, and for best results, aim to keep them between 10°C to 30°C
What happens if I overcharge batteries?
OVERCHARGING is one of the worst things that can happen to your battery, but is unlikely with a high quality charge controller.
During overcharging, excessive current causes the oxides on the plates of the battery to "shed" and precipitate to the bottom of the cell, and also heat the battery, thus removing water from the electrolyte. Once removed, the oxides (which represent capacity) are no longer active in the battery. In addition, the loss of water from the electrolyte may expose portions of the plates, and cause the exposed areas to oxidize and become inactive, thus reducing capacity even further. Sealed batteries are not immune to these dangers of overcharging. In fact, sealed recombination absorption and gel batteries are particularly sensitive to overcharging.
Luckily all our charge controllers are configured to charge our batteries at the optimal settings for the fastest charge without overcharging to get the longest life out of the batteries, so you won't have to worry about this.
What happens if I over-discharge batteries?
OVER-DISCHARGING over-works your batteries. Discharges deeper than 50% (below 12.0V) significantly shorten the Cycle Life of a battery. Infrequent or inadequate recharging (leaving them partially charged or not filling them up to 100% each cycle) can also cause rapid sulfation – a buildup of lead sulfate crystals covering the battery plates. This coverage deteriorates the overall efficiency and power storage capability of the battery, meaning over-discharging and inadequate recharging will result in a loss of battery capacity.
How can you check a battery’s performance?
As a battery gets older, it will not have the same amount of capacity it had when it was brand new. To test the capacity of the battery, you will need to discharge the battery using a constant draw. By knowing how much current is being drawn, measuring the voltage at the beginning and at the end of the test, and timing the test, you can calculate the batteries capacity. This can be a complex test, and should only be done if you suspect the batteries are failing.
Keeping your deep cycle battery in good condition is pretty easy when you know the basics and take the time to look after them carefully. Still got questions about solar battery maintenance? Feel free to leave a comment or get in contact with us and we’ll help you find an answer!