Solar Reg

Any recommendations for a cheap solar reg for use on a 20 or 40 watt panel to maintain a 12 volt battery.

The battery is the start battery for a genset that has an auto start function. Unfortunately, if a start has not been requested over the period of 4 to 5 days, the standby of the auto start function drains the battery.

I see there are heaps of cheapies on Ebay,,, so any recommendations?

That one looks ok, but at that price is almost certainly a basic PWM type. But you can get an extra 30% charge or so out of your panels if you opt for an MPPT type regulator. You can pay hundreds for these, but there are many cheaper ones on the market that work well. paid a bit over $100 for a "Tracer" brand via eBay about 5 years ago and it works very well. Search for "Tracer MPPT solar controller" and you'll get a heap of purchase options.

Or, if you just want a cheap trickle charge solution, you could connect a small panel directly to the battery - something with a watts rating of about 5% or less of the battery Ah capacity (eg 5W for a 100Ah battery). Much more panel wattage and you run the risk of overcharging on sunny days. But a regulator of some sort is better.

Cheers, Graeme