Product Overview The TR24 is a current-sampling RV battery monitor — a coulometer rather than a voltmeter. A matched shunt is bolted in series with the battery pack negative, and every amp that enters or leaves the pack passes through it. The 72.5 mm round gauge samples that current continuously and converts it into state of charge, remaining capacity in Ah, and remaining charge or discharge time — the figure most owners actually need before deciding whether to leave the