If you find that the inverter battery bank is draining faster than usual or just drained – could the inverter be the reason that the battery is draining fast? And if so, how much an inverter contributes to the power draw from the batteries?
This post seeks to explain that – whether inverters drain the battery, how much of a drain they contribute, what drives the drain, and lastly shares tips to protect the batteries from being deeply discharged.
Can an inverter drain the battery?
Yes, a power inverter in standby mode can drain the battery with no appliance plugged in or switched on provided the inverter power switch is on. This is not limited to car inverters but can happen to RV inverters.
For example, as a guide, a 1,000-watt/ 12V inverter with a no-load power consumption of 7.5W continuously draws 7.5W or 0.63 Ah of the battery capacity even when the no appliance is connected.
Granted, the drain on the battery by an efficient inverter will be a fraction of what it draws at full power but over time, it amounts to considerable power draw and can drain a car battery flat. The drain on the battery by an inverter mainly depends on:
- the inverter efficiency (%) – a more efficient inverter will have a smaller current draw
- Inverter capacity (watts) – large capacity inverters usually have a larger current draw in standby mode than the smaller capacity inverters
The current and power draw of an inverter on standby
To find the specific current or power draw for your inverter model, refer to the technical specifications section of the inverter’s owner manual. Usually, manufacturers list the no-load current only.
To work out the no-load power draw, simply multiply the current by the battery voltage.
For example, a 12V inverter with a no-load current of 400 mA draws about 400 mA x 12V = 4.8 watts when in standby mode.
How Long a 12V Battery Lasts with an Inverter
There’s no one answer as to how fast a battery will drain when connected to an inverter in standby mode as there’re several variables at play such as:
- the power inverter’s no-load power consumption
- The battery capacity (Ah), and
- Its state of charge.
Take, for example, a 1000-watt/12V inverter with a no-load power consumption of 7.5 watts connected to a fully charged 100 Ah AGM battery.
With no load connected, the inverter will drain the battery to 50% of its capacity in 80 hours or 3.3 days.
The calculation
Battery runtime = ((Available battery capacity, 100 Ah) x (depth of discharge, 50%)x (battery voltage, 12V))/ (no load inverter power consumption, 7.5 watts).
What Causes an Inverter Battery to Discharge Quickly
If the battery(s) appears to be draining faster than usual, check:
1. there are no appliances running that may have been accidentally left ON. In some cases, the batteries appear to be draining fast because of additional appliances switched ON.
2. that the inverter batteries are fully charged. It is possible that the inverter batteries are only partially charged or not charged at all creating the mistaken impression that it is draining faster than usual.
Are the battery terminals clean and firmly connected to the alternator or charge controller?
If using solar, does the charge controller show a fully charged status of the battery? confirm that the charging source – the charge controller, battery charger, or car’s alternator is actually supplying power to the battery.
You can:
- use a good quality digital voltmeter set to read volts to measure the battery voltage. A fully charged battery has a resting voltage of about 12.65V.
- can use a clamp on current meter to measure the current flow to the battery to confirm that indeed the batteries are charging.
3. The batteries may be aging and have lost their capacity to hold charge. Does the battery voltage drop considerably over 1-2 hours after full charge with no appliances connected? For example, from 12.6 – 12.4V? How old are the inverter batteries?
For example, While some batteries can last for 5+ years, several AGM batteries last for about 3 years only. So it is possible that the batteries are on their last legs and should be replaced!
Tips to Stop an Inverter Battery from Draining Fast
To limit the power draw of the inverter when in standby mode, you can :
- Switch it OFF when not in use.
- Switch on the power saving mode (available on selected inverters). Some inverters have a power-saving mode that can reduce the standby power draw by as much as 80% when activated.
Avoid using inverters with a higher power rating (watts) compared to the connected appliance’s power consumption. The no-load power consumption can be significant in comparison to the appliances powered.
How to Protect a Battery from Deeply Discharge
- You can also install a programmable low-voltage disconnect switch that disconnects the inverter at a higher voltage before the battery is fully drained.
- Switch off the inverter when not in use.
- If the inverter has power saving mode, switch it on to reduce its drain on the battery and extend how long the battery lasts.
Why you Shouldn’t Rely on an Inverter Low Voltage Disconnect
Inverters usually have a low voltage disconnect feature that shuts it down as low as 10.5V DC. Unfortunately, the low voltage disconnect voltage is usually set at too low a voltage.
By the time it is triggered, the battery is usually completely drained. To stop the inverter from draining the battery when no appliance is connected, switch it off.
Can an Inverter kill the Battery?
Yes, an inverter could possibly damage a battery even in standby mode by drawing the battery power below the recommended depth of the battery.
There can be several contributing factors to whether or not a battery will be damaged. For example, the likelihood of damage increases in the case of :
- An aging battery will likely suffer damage than a newer battery
- If the battery is deeply discharged repeatedly
Note: Battery lifespan reduces when they are deeply discharged repeatedly beyond the recommended depth of discharge, 50% for AGMs and 80-90% for LiFEP04.
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Why an Inverter Battery May Be Draining Quickly
If the inverter battery does not last or drains overnight then it might be that:
- there are appliances left switched on that continue draining the battery,
- batteries are not charged fully, or
- the batteries are aging. It is worthwhile investigating each of the above possibilities first before you invest in a new battery.
Closing Thoughts
An inverter can drain the battery if left switched ON. The power draw largely depends on the inverter’s efficiency and inverter capacity. More efficient or smaller inverters tend to have a lower power consumption when on standby compared to inverters with a larger capacity rating.
To stop the current draw, switch off the inverter when not being used. You can limit its no-load power consumption by engaging its power-saving mode setting (if it has that feature).
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