As I use my car rarely over the winter months, in January this year I installed a 40 watt solar panel connected to a PWM controller and this fed my new Varta car battery via an internal cable to my diagnostic socket. I then bought a diagnostic plug and soldered the cable to the positive and negative pins. Prior to the connection I checked the draw was 30mah. But after 3 months I discovered the battery was down to virtually no volts. I removed the battery and put it onto a mains trickle charger expecting it not to recover. I then discovered how the discharge happend, the PWM controller was dead and oxidised after disassembly. It was discarded and replaced with a Victron MPPT Smart controller. The Varta battery on charge recovered to max volts. Left the Varta off charge to see how long those max volts of 12.76 would last. A month later it still showed 12.66v on voltmeter. So added the battery to the car and monitored the solar charge now via Bluetooth on my tablet. I had added quick solar plug/sockets to the controller so I could disconnect to use the car, but on return reconnected them. All summer and autumn battery at 12..7v. But come November I noticed a small drop each week of battery voltage and now today 7th December down to 12.18v. Now my dilemma, is the Varta battery on the way out having endured a total loss last winter? Would a larger solar panel resolve the charging over limited sun in winter? I chose Victron 40 watt solar panel from results of reviewers saying in the Northern Hemisphere this should be sufficient. Any views on help on this would be appreciated.
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