MiniDisc Gumstick Battery FAQ
Gum/gumstick/flat batteries - how to charge them and determine their condition
1) What is a gumstick battery?
A gumstick battery is a type of rechargeable battery that was introduced in the 1990's, primarily for use in portable audio equipment. Gumstick batteries have a much smaller form factor than typical AA and AAA batteries, and have equal to, or greater charge capacity. As such, they are well suited to devices like portable cassette and MiniDisc players.
They are known as, 'gum', or, 'gumstick', batteries because their shape resembles that of a packet or stick of chewing gum. They are less commonly known as flat batteries.
2) What are the different types of gumstick battery?
The two main types are Ni-Cd (Nickel-Cadmium) and Ni-MH (Nickel-Metal Hydride). Ni-Cd gumstick batteries are the first generation and are now very difficult to find in good working condition.
Ni-Cd gumstick batteries were superceded by the Ni-MH variation, which are less damaging to the environment, enable a greater total charge capacity, and are more durable. Ni-MH batteries can have two to three times the capacity of Ni-Cd batteries of the same size.
3) A lot of these batteries were manufactured over twenty years ago. Are they still usable?
It depends, but if the battery is in good condition, then yes!
4) Are these batteries still being manufactured?
Yes. The gumstick batteries that were sold with portable audio players usually bore the brand of the manufacturer, such as Sony, Panasonic, Sharp, and Victor (JVC).
At the time of writing this (November 2024), gumstick batteries are still being manufactured; primarily by Chinese companies.
5) Are all gumstick batteries equal?
Based on personal experience, I would say no. Even if the spefications of the batteries as stated to be equal, or in some cases better (greater capacity), the actual performance and durability of batteries will differ.
You may think that a brand new battery would perform better than a used one, manufactured 20 years ago, but it's not always the case. Ultimately it may come down to personal experience and preference, but all of the batteries I use on a regular basis are probably more than 20 years old.
6) OK, so gumstick batteries are an unusual type of rechargeable battery, but how do you charge them?
There are 2 main methods to charge a gumstick battery:
- In a dedicated battery charger
- By inserting the battery into a portable audio device, and then placing the device on a battery charging stand, or connecting the device to mains power with an AC adapter
Investing in a dedicated battery charger, that is confirmed to work with gumstick batteries, is the most flexible option and is the best choice if you plan to own more than one portable audio device. Battery charging stands are usually unique to the device it was designed to work with. AC adapters have some interoperability, but most vintage portable audio devices don't have a socket to allow direct connection of an AC adapter.
7) How do you define when a gumstick battery is in good condition?
It is defined by the actual charge capacity, and how much of that charge can be discharged.
Gumstick batteries are all rated at 1.2 volts. Any gumstick battery that can be charged will register at least 1.2V on a tester. This is NOT a measure of battery performance. Ni-MH batteries will maintain at least 1.2V until the charge is depleted.
Actual battery capacity is measured using mAh (milliampere per hour). The greater the charge and discharge value in mAh, the longer it will be possible to use the battery without having to recharge it.
To make this simpler, think of a bathroom shower. Think of the voltage as the water pressure, and the mAh as the amount of water in the tank. Without water pressure no water will come out of the shower, and without water in the tank there's nothing there to wash with. The more water in the tank, the longer you can shower for.
Generally speaking, a gumstick battery will continue to work until the charge (mAh) is depleted. Having said that, most batteries will actually discharge less than the charge value. Therefore, battery charge capacity (mAh), not voltage, is the way to measure battery health.
8) OK, so how should I identify a battery in poor condition?
If possible, get the charge and discharge values in mAh. If the discharge value is significantly less than the charge value, it's likely that the battery is nearing end of life and, while still usable, will continue to deteriorate.
For example:
Charge 900 mAh
Discharge 450 mAh
In this example, it's still possible to get a good charge into the battery, but discharge is very inefficient in comparison.
9) Do all gumstick batteries have the same maximum capacity?
No. Generally speaking, the early Ni-Cd versions started at 600 mAh capacity, and the later Ni-MH batteries went up to 1400 mAh capacity. Gumstick batteries being manufactured at present are usually rated at 1450 mAh capacity. Of course, these are only target values, and just because a battery has 1400 mAh written on the casing does not necessarily mean it will take a charge of 1400 mAh.
10) How do I know if my gumstick battery has reached end of life?
Assuming the use of a good quality battery charger, the battery will only take a small charge (much less than the rated capacity), or it simply won't be possible to charge the battery at all.
11) How can I keep my gumstick battery in good working condition?
Don't leave it in a device for a long period without use as it will leak, which can permanently damage the equipment.
Invest in a good battery charger.
Use the battery regularly. A lot of the time, battery performance will actually improve with correct, regular usage.
If you don't plan to use the battery for a long period of time, then don't leave it fully charged. For an Ni-MH battery, approximately 40% of total, actual battery capacity is recommended for a storage charge.
Summary
Gumstick batteries are a legacy technology that were mainly used in portable audio devices. They are still being manufactured, and even batteries that were manufactured more than 20 years ago can function well if they have been well cared for.
A dedicated gumstick battery charger is arguably the best option for charging gumstick batteries.
The way to measure actual battery performance is by confirming the charge and discharge values in mAh.
Actual battery performance can be tested with a higher-end battery charger.
Hopefully this information is clear and covers everything you need, but don't hesitate to reach out if you have any questions.