Batteries
Contents: Batteries
Rechargeables
• Self-discharge rate
• Voltage
• Chemistry, NiMH, Li-Ion, NiCd
• Capacity
Chemistry settings
Disposable batteries
Mixing batteries
Batteries
Some purpose-built handhelds contain integrated captive batteries which can last very well on a full charge. Garmin claim up to 180 hours for the GPSMAP 67.
Other handhelds will run on AA batteries. The Garmin eTrex, 64 and 65 units will all run on two rechargeable AAs. If you’re off on a long day, a spare pair of AAs weigh little and could provide at least 16 hours of extra use with these models. A great advantage over a smartphone.
What are the best batteries to use?
Rechargeables
These are a good choice for powering GNSS handhelds. They are more expensive to buy than disposable batteries like the familiar copper top Duracells. However, they are much better value in the long run. They will last for years and manufacturers claim they can be recharged hundreds of times. You can be sure of having fully-charged batteries for your outing.
Apart from getting the right physical size (usually AA), there are four key things to consider when choosing batteries for GPS handhelds…
• Self-discharge rate (low)
• Voltage (1.2v or 1.5v)
• Chemistry (NiMH or Li-Ion for winter)
• Capacity (800mAh – bad, 2500mAh – good)
Self-discharge rate
When a battery is not doing anything it slowly loses its charge. Some rechargeables can lose their charge quickly and always seem to be flat when you want them. Buy batteries with a low self-discharge rate and you’re less likely to get caught out.
They might be called pre-charged or hybrids. The manufacturer’s website will normally mention their discharge rate. These can be left for many months before using and still hold useful charge.
Voltage
Rechargeable AA sized batteries come in 1.2v, 1.5v and less common, 3.7v. Don’t use the 3.7v batteries as you could blow up your device. However, the AA powered Garmins and the Satmap Active 20 were designed to work with 1.2v or 1.5v batteries. Both work well.
Capacity
Obviously, you want the batteries in your GPS handheld to last as long as possible. The higher the capacity of the battery the better. All other things being equal, high capacity 2400mAh batteries will keep your device running for three times as long as low capacity 800mAh batteries.
Which battery has the highest capacity isn’t always obvious as battery capacities are rated in two different ways. Rechargeables with a Nickel Metal Hydride chemistry (NiMH) tend to be rated using milliamp hours (mAh) and those with a lithium chemistry are more often rated in milliwatt hours (mWh).
mWh is a measure of exactly how much energy is stored in the battery.
mAh is a measure of how much current can be supplied by the battery at its rated voltage.
The two aren’t quite the same as a 1.5v, 2000mAh battery contains more energy than a 1.2v, 2000mAh battery. 3000mWh vs 2400 mWh. You can make approximate conversions between the two to see how batteries compare. The arithmetic is simple.
Convert mAh to mWh
Multiply the mAh capacity by the battery voltage.
eg An Eneloop Pro 1.2v, 2500mAh rated NiMH battery.
1.2 x 2500 = 3000mWh
Convert mWh to mAh
Divide the mWh capacity by the battery voltage.
eg A Hixon 1.5v, 3500mWh rated lithium-ion battery.
3500 ÷ 1.5 = 2333 mAh
The two batteries in these examples have similar capacities and the Hixon battery will deliver electrical current (milliamps) at a higher voltage. The only way to know for sure how they’ll compare in your device is to try them.
Chemistry
Nickel Metal Hydrides (NiMH)
These are the most used today and if you grab a set of rechargeables off a supermarket shelf they will likely be NiMH batteries. You might notice that the voltage rating on these is 1.2v not the 1.5v we’re used to seeing with disposable batteries like Duracells. That’s a function of the NiMH chemistry.
Most devices that are designed to run using 1.5v batteries will work fine with 1.2v batteries too. The Garmin and Satmap handhelds all support these 1.2v batteries. NiMH batteries work well in most situations and don’t suffer much from the memory effect like old nicads.
Capacities vary from as low as 800mAh to 2800mAh. Get the highest capacity, low self-discharge rate batteries you can afford.
The Panasonic Eneloop Pros are well made, rated at 2500mAh and last for years. The Eneloops have a low self-discharge rate. They’ve got a good reputation. I’ve used Eneloops for years with few problems. Panasonic claim they can be recharged 500 times.
Duracell have a similar product (HR6). Another 2500mAh rechargeable NiMH battery with a low self-discharge rate.
Some higher capacity NiMH AAs may have a high self-discharge rate. eg EBL do a 2800mAh NiMH battery that discharges faster than the Eneloops. I’d avoid these. They tend to be flatter than you want when you need to grab a couple.
The output voltage gradually reduces on these batteries whilst they are powering your handheld. When the voltage gets too low the handheld will stop working. That will happen sooner in the winter cold. NiMH batteries should work through a UK winter but they won’t last so long. Take spares and keep those spares warm until they’re needed.
Lithium-ion (Li-ion)
These are the most expensive and a relatively recent battery development for 1.5v AA rechargeables. Li-ion is the best of all the battery chemistries.
They are the best performing in very cold and very hot temperatures. They deliver the full 1.5v that we’re used to with disposable batteries and they maintain that voltage well until they fail. They have a very low self-discharge rate and can be recharged many times. EBL claim 1200 recharge cycles for their batteries. They don’t suffer from the NiCd ‘memory effect’ and some models can be charged more quickly than NiMH batteries too. They are also lighter for any given battery capacity.
The largest capacity rechargeable Li-ion AAs are currently around 3500mWh (2333mAh).
Lithium is a very reactive metal and will burn, so don’t try charging a Li-ion with a standard NiMH battery charger, you risk overheating, fires and explosions. Ensure the Li-ion charger you use with any Li-ion batteries is perfectly compatible. Often Li-ion batteries are supplied with their own charger.
Unusually, some of the Lithium based rechargeables have micro-USB ports built into the battery along with electronics to manage the charging and power delivery.
You can charge one with a normal USB to microUSB lead that you might have lying around. You can charge four at once from a single USB port using a lead with 4 micro-USB plugs all wired to a single regular USB plug. EBL can supply these with a pack of four.
There are few disadvantages to lithium-based batteries but an internal short circuit between the positive and negative electrodes allows a lot of energy to flow quickly. The result can be heat and fire. The Samsung Galaxy Note 7 had to be recalled as a battery fault was causing the phones to burst into flame. It’s probably a good idea to avoid unknown brands on Amazon and eBay.
Good quality lithium batteries should be a good choice particularly for winter use. It’s no accident that smartphones, the Satmap Active 20 battery pack and the Garmin units with built-in batteries all use lithium-based batteries.
Nickel Cadmium (NiCd)
Avoid. Commonly known as nicads. Total battery capacity is poor and they use old technology with particularly nasty chemicals. Unless these are fully discharged every time you use them, they tend to remember where they were last discharged to. This ‘memory effect’ causes their capacity to reduce significantly over time.
Chemistry settings
The different battery types discharge differently. For the battery meter on your device to give a meaningful reading it needs to know what batteries it’s being powered by. Choose the right battery type in the device settings.
Disposable batteries
If you can’t use your rechargeables for any reason then these should work well. They have extremely low self-discharge rates and may retain a good amount of charge for years. They can also provide good capacities too.
Alkaline disposables like the familiar copper top Duracells have a water-based electrolyte in the battery that can freeze in really cold weather and they are more likely to leak. The voltage also drops steadily as they discharge. Not the best choice for serious winter use but fine when it’s not freezing.
The Duracell LR6/MN1500 Plus Power alkaline batteries are 1.5v, 3000mAh capacity batteries. A pack of four will be much cheaper than equivalent rechargeables but once they’re flat they’re only any good for the recycle bin.
As with rechargeables, lithium-based disposable AAs are first choice for winter use and perhaps the longest lasting AA batteries you can put in a handheld. They may also hold their charge for many years but they are expensive. The ‘Energizer Ultimate Lithium’ is a 1.5v 3000mAh capacity battery.
Mixing batteries
When popping a pair of batteries into a device the two batteries should be the same type and of similar age. Putting a brand new battery in alongside a knackered battery is not good for the batteries or your usage time.