Clampmeter with DC amps range for $50.
https://www.amazon.com/Multimeter-BTMETER-BT-570C-APP-Resistance-Temperature/dp/B07CFWL3SY/ref=sr_1_25?keywords=dc+clamp+meter&qid=1569816381&sr=8-25
Uni-T brand for about $50.
https://www.ebay.com/itm/UNI-T-UT210E-Digital-Clamp-Meter-Multimeter-Handheld-RMS-AC-DC-Mini-Resistance/303171177473?epid=10024590837&hash=item4696690c01:g:~UcAAOSwNqRcLYXX
I have had a Uni-T brand for about the same price for years and it works perfectly.
Careful going lower in price - it may only measure AC amps. Measuring DC amps without contact requires a very special Hall Effect sensor to measure the tiny magnetic field that circulates around a current flowing in a wire.
My batteries apparently died overnight in the first year of use on a long trip. I was using the idiot lights and voltage readings to get the state of charge. The thing is the voltage on the battery is what the charging voltage was for hours so the voltage method can be overly optimistic for hours after any charging. I thought engine charging was keeping the batteries fully charged but it wasn’t. The solution is a battery monitor that counts amp-hours going in and out of the batteries to calculate the per cent of full charge.
I have a $30 one from eBay that works very well.
https://www.ebay.com/itm/DC-120V-100A-Battery-Monitor-State-of-Charge-Remaining-Capacity-AMP-Voltage-AH-/182147916411?hash=item2a68dca27b:g:gWUAAOSwyQtVz1vp
