Rick, Solar panels do degrade, about 1% per year, so yours might be down to 75 or 80% of original output by now. One thing, say you have a 100 watt panel, it will produce about 5 amps of charge current for about 5 hours per day in full sun, no clouds or shading by trees. So that is really only a 1 amp trickle charger, if you take the 25 amps output over a whole day. One other rule of thumb is that you will see about 75% of panel output at your batteries in real time; this accounts for all losses, from high ambient temp, occasional high clouds or smog, wire size, etc. So your 20+ year old panels will make about 75% x 75% or for a 100 w panel that equates to about 56 watts accounting for all losses. So the long and short of it is solar panels are great but don't expect them to keep your batteries charged.
