Welcome to Quadcrazy @Maxx. Oil levels in the gauge/sight glass wont be accurate when running. Oil is consistently flowing through the engine so its never all in the same place for an accurate oil reading. If your not getting an accurate reading then its safe to say its ok. Engine off, wait 15 minutes and take an oil reading. You will be at 97% accuracy of your dipstick or sight glass. The other 3% is still in the head or lining the engine walls. As far as battery ratings; go on Amazon, there are tons so have at it. I personally like the pirate battery.
YTX5L-BS Replacement Motorcycle Battery - Rechargeable High Performance - AGM - Sealed Maintenance Free - Pirate Battery https://www.amazon.com/dp/B06XDRYQLZ/ref=cm_sw_r_cp_api_i_vCEWEbG7WTPD0