Originally Posted by maurerl
Battery is usually fully-charged by approx 10 - 11 AM each day. And "loses" power all during remainder of day, despite being in full unshaded sunlight. Would usually be down to around 50% by bedtime, despite using no power during the day?
To my untrained (in these matters!) mind, this suggests either something draining the batteries during the day (but we're not using anything!) or the batteries not holding their charge. Am I right?
On Reace's advice, checked the batteries with a hydrometer, and all six cells (dual 6-volt batteries) are showing specific gravity around 1.25 - but I have no idea how to "interpret" that.
Is it time to buy new batteries? Batteries are ~ 4 years old.
Sometimes a simple volt meter can answer your question. Once my batteries have been charged by the panel the voltage still remains above 13 volts even as the sun fades. It stays there until the surface charge is taken off by the first use of a load such as the water pump or a light. Then the true battery voltage is visible, usually 12.7 volts. There is no way the battery voltage will drop down to 50% etc. if no heavy load is being used.
A meter like this is about 5 bucks on ebay. I'd recommend using one of this type or a hand held multi-meter to independently check what's happening with your batteries.