battery?
I would start by lifting the negative cable from the post of each battery. Check the electrolyte level of each cell in each battery and bring it to the proper level by adding distilled water(not demineralized). The charge the batteries with a good, three state battery charger. Once charged, let the battery sit for 8 hours or so, with the cable still lifted and then check the resting voltage. It should be about 12.7V or so by a quality digital meter. Then allow the battery to sit for another 24 hours and check it again. It should not have dropped any more than 0.2V, maximum. Do the same for several days. If the voltage keeps falling, the battery has a problem. If it does not stabilize at some point at or above 12.5V it is probably time to think of a new one. You can also have a battery load tested at your local battery shop.
________________________________________________________________
Percent -- Voltage-- Specific
Charge ********* Gravity
100 -- 12.70 -- 1.265
-95 -- 12.64 -- 1.257
-90 -- 12.58 -- 1.249
-85 -- 12.52 -- 1.241
-80 -- 12.46 -- 1.233
-75 -- 12.40 -- 1.225
-70 - - 12.36 -- 1.218
-65 -- 12.32 -- 1.211
-60 -- 12.28 -- 1.204
-55 -- 12.24 --- 1.197
-50 -- 12.20 -- 1.190
-45 -- 12.16 -- 1.183
-40 -- 12.12 -- 1.176
-35 -- 12.08 -- 1.169
-30 -- 12.04 -- 1.162
-25 -- 12.00 -- 1.155
-20 -- 11.98 -- 1.148
-15 -- 11.96 --- 1.141
-10 -- 11.94 -- 1.134
-05 -- 11.92 -- 1.127
-00 -- 11.90 -- 1.120
Based on use of 50% battery capacity.
True full discharge eqaual 10.5V