Leaking battery in a pinball machine: dangers, damage and the definitive fix
A leaking battery is the number one cause of death for vintage pinball circuit boards. As it ages, the backup battery soldered onto the CPU board leaks alkaline potassium hydroxide, which eats away at the traces, components and connectors. The good news: the damage can be cleaned and repaired, and there is a definitive fix so you never have to think about it again — a battery-free replacement board. Here is everything you need to know.
Contents
- Why is there a battery in a pinball machine?
- Why does the battery leak?
- The damage from a leaking battery: corrosion, NVRAM, lost scores
- How to spot a board attacked by acid
- Cleaning and neutralising corrosion, step by step
- Remote battery, capacitor or battery-free board: which to choose?
- The definitive fix: a battery-free replacement board
- FAQ
Why is there a battery in a pinball machine?
On solid-state pinball machines (from around 1977 onwards), a small backup battery powers a volatile RAM when the machine is switched off. This memory holds the game settings, the bookkeeping (audits) and the high scores. Without it, the CPU board would forget everything at every power cut.
Depending on the manufacturer, this was a rechargeable 3.6 V Ni-Cd accumulator or alkaline cells. Gottlieb System 1 boards use a rechargeable “DataSentry” battery or a 3.6 V AA Ni-Cd cell. On Bally/Stern machines from 1977-1985, the battery is soldered directly in the middle of the MPU board (typically a pack of three AA cells). It is precisely this “on-board” mounting that causes trouble decades later.
Why does the battery leak?
A leaking battery in a pinball machine is nothing unusual: it is the almost inevitable fate of a battery twenty to forty years old that has never been replaced. Over time the seal degrades and the electrolyte escapes. Two factors accelerate the phenomenon:
- Age. Removing a rechargeable battery more than twenty years old is considered a mandatory repair by specialists.
- Lack of use. A machine that is stored and rarely switched on sees its battery discharge, swell and then leak. The volatile gases and alkaline potassium hydroxide that escape then attack the neighbouring components and connectors.
In other words: it is not a question of “if”, but of “when”. Any original board still fitted with its battery is a time bomb.
The damage from a leaking battery: corrosion, NVRAM, lost scores
Alkaline electrolyte is extremely corrosive. Once it escapes, it first oxidises the metal tabs of the holder, then migrates along the copper traces by capillary action. The consequences are gradual but serious:
- Corrosion of traces and components: characteristic green or grey deposits, eaten-away traces, attacked IC legs.
- Destruction of the memory (RAM/NVRAM): the backup chip and its socket are often the first hit. The result: lost settings and high scores, erratic game behaviour.
- Spread to the connectors: on Bally/Stern, the corrosion can reach connector J4 and slip underneath it. As this connector carries 43 V, even a small amount of corrosion can bleed that 43 V onto the 5 V bus and destroy every chip on the board.
- Damage that spreads to other boards: an untreated source board can, in time, damage the boards connected to it.
Let us be honest: a leaking battery is a purely electronic problem. A replacement board fixes it for good. However, it does not correct mechanical problems (coils, targets, mechanisms) or playfield wear: those are separate matters.
How to spot a board attacked by acid
Before buying any used pinball machine, open the backbox and inspect the CPU/MPU board. Look for:
- white, green or grey deposits around the battery or its holder;
- a swollen battery or one that is visibly old and still soldered to the board;
- darkened traces, blistered or broken;
- tarnished or greenish connector pins.
On Gottlieb System 1, a simple check is to measure the voltage at the backup RAM (5101): between 4.1 and 4.5 V DC means the backup supply is fine. Below that, the battery is at the end of its life.
Cleaning and neutralising corrosion, step by step
If the damage is limited, a board can be saved. Here is the method recognised by repairers:
- Remove the board from the backbox and immediately desolder the old battery (to be recycled).
- Identify the damaged components (green/grey traces). Cut their legs then remove them; replace any doubtful chip or leg.
- Check the connector pins: if greenish, they must be replaced.
- Sand the oxidised areas down to bright copper.
- Neutralise the acid with a mix of white vinegar + water (50/50), scrubbing with a toothbrush. A crucial step: without neutralisation, the corrosion comes back.
- Rinse with clean water, then with 99% isopropyl alcohol (which drives out the water and dries fast).
- Re-tin the sanded traces, refit the components on quality sockets, then reset the audit memory.
It is effective, but long, messy and reserved for those comfortable with a soldering iron. And above all: if you fit a fresh battery, you are off for another round… with the same risk of leaking in a few years.
Remote battery, capacitor or battery-free board: which to choose?
Three approaches exist to prevent a battery from leaking on your board again. Here are their pros and cons:
| Solution | Principle | Advantages | Limits |
|---|---|---|---|
| Remote battery holder | AA cells off the board, connected by wires, with an anti-charge diode | No more leaking on the board; keeps the memory for a long time | Modification requires soldering; the cells still need monitoring and replacing |
| Backup capacitor (1 F) | A capacitor replaces the battery and recharges at power-on | Never leaks, does not degrade | The machine must be switched on ~1 h/month; initial charge ~8 h; variable autonomy (from a week to several months) |
| Battery-free replacement board | A modern (FPGA) board replaces the original electronics, with no battery at all | Zero corrosion, Plug & Play, lasting reliability, memory kept with no maintenance | Higher initial investment than a simple battery |
The remote holder and the capacitor limit the risk, but require either monitoring or regular maintenance. The only approach that removes the problem entirely is to take the battery out of the equation.
The definitive fix: a battery-free replacement board
At Pinballs Store, our modern replacement boards (FPGA-based) faithfully reproduce the original electronics with no battery at all. The memory is kept by non-volatile electronics: no more battery, so no more leaks, no more corrosion and no more lost scores. They are Plug & Play (no soldering), supplied with free technical support in French and a 15-day satisfied-or-refunded guarantee.
Depending on your machine, the right board differs:
- Gottlieb System 80 / 80A / 80B: the all-in-one GottFA80_Plus board redoes CPU, driver and power supply. See also the System 80 guide and the Lisy80 for diagnostics.
- Williams System 3 to 7: the WillFA7 board. Details in the Williams guide.
- Bally/Stern 1977-1985: the BallyFa CPU board. See the Bally/Stern MPU guide.
To go further on choosing between repair and replacement, also read our article: Repair or replace a pinball circuit board?
Put an end to the leaking battery — from €349
The all-in-one GottFA80_Plus board for Gottlieb System 80/80A/80B replaces the original CPU, driver and power supply, with no battery: never any corrosion again.
- ✅ Plug & Play — no soldering
- ✅ Battery-free — zero leaks, memory retained
- ✅ Free technical support in French
- ✅ 15-day satisfied-or-refunded guarantee
FAQ: leaking battery in a pinball machine
How do I know if my pinball battery has leaked?
Open the backbox and inspect the CPU/MPU board around the battery. White, green or grey deposits, a swollen battery or darkened traces are clear signs of leaking. On Gottlieb System 1, a backup voltage below 4.1 V indicates a battery at the end of its life.
Can a leaked battery destroy the whole board?
Yes. The electrolyte migrates along the traces and can reach the connectors. On Bally/Stern, the corrosion can bleed the 43 V from connector J4 onto the 5 V bus and damage all the chips. Treating it early limits the damage.
How do I clean battery corrosion on a pinball board?
Desolder the battery, replace the attacked components, sand the copper, then neutralise the acid with a 50/50 white vinegar/water mix. Rinse with clean water then 99% isopropyl alcohol, re-tin and reset the audit memory.
Should I fit a fresh battery after cleaning?
You can, but the risk of leaking will return in a few years. The alternatives are a remote battery holder, a backup capacitor, or — the definitive fix — a battery-free replacement board.
What should I do if I lose my settings and high scores?
They are stored in the memory backed up by the battery: a dead or removed battery erases them. After repair or fitting a modern board, redo the settings; a battery-free board will then keep the memory with no maintenance.
Does a battery-free replacement board fix the problem for good?
Yes, for the electronic part linked to the battery. With no battery, there is nothing left that can leak or corrode. However, it does not repair mechanical faults (coils, mechanisms, playfield), which are separate maintenance matters.
