Battery percentage jumping up and down
Why is my battery percentage jumping up and down?
Seeing erratic battery percentages in your solar app? If you have two or more batteries, sudden drops or unexplained spikes usually mean they have fallen out of balance.
Although it can look alarming, in most cases nothing is broken. The batteries simply need to be rebalanced and re-synced, which is normally a quick job for your installer. This page explains what is happening and what we will do to put it right.
How to tell if this is your issue
Check for these signs:
This behaviour is most common on systems with two or more batteries working together as one bank.
The percentage drops sharply when it reaches roughly 30%, for example from 30% down to around 10% in one step.
The percentage can also jump the other way, for example from 90% straight up to 100%.
The change happens within a single 5-minute window in your monitoring data, which is not normal battery behaviour.
If these signs sound familiar, read on. If you are not sure whether this matches your system, please contact us and we will help you confirm before anything is done.
Why does this happen?
Multiple batteries work together as a team, but each one has its own Battery Management System (BMS). For the system to report a single battery percentage, the batteries need to stay closely balanced with each other. When they drift out of balance, the system can lose sight of one of them.
- At low charge — for example, when your batteries discharge to roughly 30%, one battery can reach its protection cutoff slightly before the other and switch itself off.
- Communication is lost — once a battery switches off, its communication link with the inverter is lost, so the system can only see the remaining battery.
- The reading drops — the reported percentage suddenly falls to what the remaining battery shows, for example around 10%.
- It can also jump up — the same imbalance can make the percentage jump upward when the batteries are near full.
The important thing to know is that your battery has not suddenly lost charge. The reading jumps because the system has lost track of one of the batteries, not because the energy has disappeared.
Is my battery damaged?
In most cases, no. Nothing is broken and no battery has lost capacity. Your batteries have simply fallen out of balance with each other and need to be re-synced.
The fix involves charging each battery to 100% on its own, checking their voltages match, then reconnecting them together so the system sees both at once. This uses installer controls and involves switching the batteries off and disconnecting them, so it is not something you should attempt yourself.
Never switch off, disconnect, or open your battery units yourself. Batteries store high-voltage DC power and must only be handled by a qualified engineer. If you are not sure what is happening, contact us rather than trying anything that could put your safety at risk or damage your equipment.
When it is a hardware issue
Less often, the imbalance is caused by a hardware fault rather than calibration drift. On some systems the batteries communicate with each other through DC-DC converters fitted to the side of the battery units. If those converters fail, the batteries can lose communication with each other and drift apart.
These signs point to a hardware fault rather than a simple balancing issue:
- The imbalance comes back, or never improves, after the balancing procedure.
- The batteries intermittently or permanently lose communication with each other.
If this is the case, the failed converters need to be replaced before the batteries can be rebalanced. We will arrange the replacement for you and return any faulty parts to the manufacturer for assessment.
What happens next
There is nothing you need to do to the system itself, and we do not recommend attempting the balancing procedure at home. Here is what happens once we are involved:
- We confirm the issue — from your monitoring data we can see whether the readings are jumping within a single 5-minute window.
- We arrange a visit — one of our engineers will attend to rebalance your batteries. In most cases this is a quick job once we are on site.
- We balance the batteries — we charge each battery to 100% on its own, check the voltages are closely matched, then reconnect and sync them together.
- Your system returns to normal — the battery percentage starts reporting correctly and stays stable, with no more sudden drops.
How long does it take?
We can normally arrange a visit within a few working days, depending on our schedule. The balancing itself is usually completed in around 30–60 minutes once our engineer is on site.
Need a hand?
If your battery percentage is jumping up and down, get in touch with your installation team at PureVolt.ie. Let us know:
- When you first noticed it — whether the jumping is constant or happens at a particular time of day.
We will take it from there. No jargon. No pressure. Just the straight answer on getting your system back to normal.
You might also find these guides useful:
- Battery charging and discharging explained — understanding normal battery behaviour.
- Battery appears dead after a power cut — what to do if your battery will not turn on.
- Solis fault codes explained — what each code means and what to check.