What Voltage Will Show on a 12v Battery As It Is Being Charged?

Updated 08/19/2025 | Published 08/07/2025

Products Featured in This Question

Trailer Breakaway Kit Battery Charger for 12V, 5-Amp Battery

(50)

$7.87

Bright Way Trailer Breakaway Kit with Charger, LED Tester, and 5 Ah Battery - Side Load

(411)

$39.94

Question:

Regarding battery charger 20011, the trailer battery became discharged after leaving interior trailer light on. I checked the voltage at the break away battery and it read 4 VDC. I started the vehicle and expected the trailer battery voltage to rise immediately to 12 VDC indicating that it was receiving a charge current. Am I wrong to expect the battery voltage to climb to 12 volts while charging or should I just check the trailer battery voltage after waiting a while? Thanks.

asked by: Stubbie

Expert Reply:

You're not wrong Stubbie. A 12v battery charging will show somewhere around 12.5 volts. If you're only getting 4 volts off of your breakaway battery you most likely need a new one. You can replace yours with the item # 3802346 kit.

For now, I recommend charging it with your current one with your Trailer Breakaway Kit Battery Charger item # 20011 and seeing if it gets back up to 12.7 volts.

Is your trailer battery connected to your breakaway battery? If so when you reconnect the Trailer Breakaway Kit Battery Charger item # 20011. I recommend connecting the black wire to the 12 volt pin on the 7-way. This way your trailer battery won't kill your breakaway battery if this happens again. Most local and state regulations require that the breakaway battery receive a charge from a battery not mounted on the trailer anyways.

How long did your trailer sit with the lights on?

expert reply by: Jerred H