Search
En
Sv

FAQ Lead-acid batteries

Frequently asked questions about lead-acid batteries

What happens when batteries discharge each other? How deeply can you discharge them without damaging them? On this page, we have gathered answers to the most common questions about lead‑acid batteries in boats – everything from charge acceptance to lifespan, top‑up charging, and how to avoid unnecessary wear. Perfect for those who want to understand more and take proper care of their batteries.

It is a measure of how well the batteries accept current. A larger battery bank provides higher charge acceptance. Older batteries have poorer acceptance.

No, as long as you have healthy batteries, only small currents flow, whose effect requires a very long time. However, a defective battery will drain even the healthy batteries in the same circuit and, over time, also damage them.

No, the starter motor lowers the voltage more than the discharged batteries and will draw all the current. If you have a diesel engine that needs to be glow‑plug heated, a small current will flow for a few seconds from the starter battery to the house bank, but it will never amount to more than 1 Ah.
After three years, many have only half of the battery capacity left. Then it may be time to replace them.
Yes. By expanding the battery bank, charge acceptance increases and the depth of discharge decreases, which reduces wear on the lead‑acid batteries. Handling when they are not in use also affects their lifespan.
To avoid drastically shortening the lifespan of your lead‑acid batteries, marine and leisure batteries should rarely be discharged to 50 percent. In normal use, you should preferably stay above 70–75 percent of the battery’s capacity. Gel and AGM batteries are more durable.
If charging continues for a number of hours at 14.4 V, the lead‑acid batteries will become overcharged. In the past, lead‑acid batteries gassed quite a lot. Nowadays, much of the gassing has been eliminated in lead‑acid batteries. Therefore, there are few boats that run the engine long enough for gassing to become a problem.

You cannot find out how much electricity your lead‑acid batteries actually contain when they are fully charged by measuring the voltage. If the lead‑acid batteries have lost capacity, you can determine this by performing a load test.

Yes, because the durability of the batteries increases if they are occasionally topped up. A solar panel can handle this for weeks while the boat is not in use.
Of course, but the downside is that you have to run around with cables across the piers and look for power outlets. A solar panel is easier.
Yes, if shore ground is not isolated from the ground in the boat.
Avoid old transformer chargers. Instead, invest in a modern charger. Large chargers charge faster than small ones, but they are more expensive. However, you rarely need a charger capable of more than 10–20 amps.