How much overnight drain is actually normal?

Enough that a small bank can genuinely be flat by morning without anything being broken. Detectors and control boards draw continuously by design. Rather than a target number, the useful test is measuring your actual standby current and comparing it against your bank size — a draw that is fine on a large lithium bank will empty a single old lead-acid battery.

My voltage reads 12.6V but nothing works properly.

Resting voltage tells you the surface state, not the capacity. A battery with badly degraded plates can show a perfectly normal resting voltage and then collapse the instant a real load is applied. That gap is exactly what load testing measures, and it is why a voltmeter reading should not be used to clear a battery.

Why is it worse in winter?

Battery capacity falls in the cold — that is chemistry rather than a fault. A bank that comfortably carries the overnight load in summer can be marginal at freezing. On lithium there is a separate and more serious issue: charging below freezing damages the cells, which is why compatible systems refuse to charge until the batteries warm.

RV battery drains overnight

What this usually means

Some overnight consumption is normal: propane and carbon-monoxide detectors, control boards and radio memory never fully switch off. The real question is whether the draw is larger than it should be, or whether the battery has simply lost the capacity to carry a normal draw overnight. Those are different problems with different fixes.

Check this first

Take a resting voltage reading after several hours with nothing charging and nothing running, then again in the morning. The size of the overnight drop, on a bank of known size, tells a technician immediately whether you are chasing a draw or a dying battery.

Drivable, with precautions

Complexity moderate

Cluster Electrical and battery

Most likely causes

Ordered by how often each one turns out to be the answer, with the tell that distinguishes it.

Battery has lost capacity with age
most common
Reads fine at rest, collapses under any real load. Often several seasons old.
Inverter left in standby
common
A frequently overlooked continuous draw, and often a substantial one.
Normal detector and control-board consumption on a small bank
common
Nothing is faulty — the bank is simply too small for the standing load.
Battery disconnect switch not isolating everything
common
Things still draw with the switch off; disconnect switches rarely cut every circuit.
Cold weather reducing capacity
common
Only happens in winter; the same bank is fine in summer.
A genuine parasitic fault
less common
Measured current with everything off is well beyond expected standby.

What you can safely check

01
Record resting voltage at night and in the morning
Several hours after charging stops, then again before anything is switched on. The drop is the measurement everything else builds on.
02
List everything that stays live with the coach off
Propane and CO detectors, radio memory, control boards, antenna boosters, and any inverter in standby. Together these explain many overnight drains without anything being faulty.
03
Switch the inverter fully off, not to standby
Standby is a continuous draw. Turning it fully off overnight is a free test of whether it is the culprit.
04
Note battery age and chemistry
Chemistry plus install date explains a large share of "bad battery" reports on its own.

What needs a technician

Load testing the bank, measuring actual parasitic current with a clamp meter, and tracing an unexpected draw through the distribution panel. Load testing is what distinguishes a tired battery from a genuine fault, and voltage alone will not do it.

Parts typically involved

So you know what a quote should be naming. We publish no prices — real costs vary by market, season and technician, and a number we invented would look authoritative and help nobody.

House battery or bank
Battery disconnect switch
Battery monitor with shunt
Inverter
Fuses and cabling

When to stop troubleshooting

A battery case is swollen, hot, or leaking
You smell rotten eggs near the batteries — that is a venting lead-acid battery and needs ventilation and distance

Can you still travel?

Drivable, with precautions

Driving is fine, but arriving with a flat house bank means slides and levelling jacks may not operate — those are the heaviest DC loads in the coach. Confirm you have enough charge to deploy and, more importantly, to retract them.

Check other symptoms against travel safety

Common questions

How much overnight drain is actually normal?: Enough that a small bank can genuinely be flat by morning without anything being broken. Detectors and control boards draw continuously by design. Rather than a target number, the useful test is measuring your actual standby current and comparing it against your bank size — a draw that is fine on a large lithium bank will empty a single old lead-acid battery.
My voltage reads 12.6V but nothing works properly.: Resting voltage tells you the surface state, not the capacity. A battery with badly degraded plates can show a perfectly normal resting voltage and then collapse the instant a real load is applied. That gap is exactly what load testing measures, and it is why a voltmeter reading should not be used to clear a battery.
Why is it worse in winter?: Battery capacity falls in the cold — that is chemistry rather than a fault. A bank that comfortably carries the overnight load in summer can be marginal at freezing. On lithium there is a separate and more serious issue: charging below freezing damages the cells, which is why compatible systems refuse to charge until the batteries warm.

Related failures

For the whole system rather than this one symptom, see RV battery and charging repair.

Next step

Work through structured triage for this system and you will end up with a written service brief: what you observed, in what order, and what has not been established yet. It is the document that lets a technician quote properly instead of guessing on arrival.

Being straight about what this is. No technician is signed to any territory yet — not one. We do not match you, dispatch anyone, or promise a call. What you get is the brief, and a request form that copies it to us so we know the demand is real. If you need someone today, take the brief and send it to a local technician directly; it works just as well that way.

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