Letter: Rechargeable Batteries and a Solar Charger

Hello HJL and JWR,

I was wondering if you could review and recommend the latest generation of rechargeable batteries available and a solar charger as well. I am leaning towards stocking up on rechargeable AA and AAA and the spacer packs that allow these sizes be used as C and D cell batteries. The vast array of options is overwhelming, and I am hoping someone with the expertise required can help. Thanks for all you do. Take care. – J.W.

HJL Replies: I have chosen to use a modular route so that I have the flexibility to charge whatever I need charged. Many of my electronics utilize proprietary batteries, but all can be charged from a vehicle (12-16VDC). I separate my solar setup from the charger so that I can attach whatever charger the item needs, to the solar module, which simply acts like a vehicle. I currently use Eneloop batteries by Sanyo. Most rechargeable batteries have a problem with internal leakage and will only hold a charge for a couple of months. Disposable batteries generally are easier to use because they can be used immediately after purchasing them. If you purchase them, you can throw them in a drawer and pull them out over the course of several years, and they are ready to go. Now with Eneloop batteries, rechargeables have the same capability. A normal rechargeable will lose about 75% of its stored charge in six months and come close to having no charge in a year. Eneloops will hold nearly 75% charge for at least three years. Because of this slow internal leakage rate, they come pre-charged in the package and are ready to go when you purchase them. Except for the higher purchase price, they have overcome practically all of the disadvantages of recheargables. Even the purchase price is tolerable if you look at the ownership cost spread out over the life of the instrument you are powering, which is reasonable since these batteries will take over 1000 charges.

Where you will find issues with your planned usage scheme is using AA and AAA batteries with adapters for C and D. Eneloop does not sell a C or D sized battery yet in the U.S., and their AA batteries are rated at 1900mAh. A decent NiMH rechargable “D” cell battery will be rated at close 10,000mAh. Eneloop has adapters to use AA in a D size, but you will loose 80% of the storage capacity in exchange for that long shelf life. (Sanyo does make them, they just don’t sell them in the U.S.)

Eneloop AAA 1800 cycle, Ni-MH Pre-Charged Rechargeable Batteries, 4 Pack

Eneloop NEW 2000mAh Typical, 1900mAh Minimum, 1500 cycle, 4 Pack AA, Ni-MH Pre-Charged Rechargeable Batteries

Alternatively, you can use the higher power model, but you get fewer charges on it:

Eneloop XX 950mAh Typical / 900mAh Minimum, High Capacity, 4 Pack AAA Ni-MH Pre-Charged Rechargeable Batteries

Eneloop XX 2500mAh Typical / 2400 mAh Minimum, High Capacity, 4 Pack AA Ni-MH Pre-Charged Rechargeable Batteries

You can also get a kit that contains adaptors from eneloop:

Eneloop SEC-CSPACER4PK C Size Spacers for use with AA battery cells

Eneloop SEC-DSPACER4PK D Size Spacers for use with AA battery cells

Eneloop adaptors are well made, but you can get adaptors to use up to 2 AA batteries to make a “D” cell that has close to 40% of the energy of an actual D cell. (65% of Sanyo’s “D” Eneloop batteries sold in Japan):

Adapter shell converts 2x AA to a D-size cell (set of two)

Chargers on the other hand are a little bit more difficult. One of the huge drawbacks to most portable NiMH chargers is that they must charge batteries in pairs. I have several items that only use one AAA battery or one AA battery, and it is a real problem keeping track of dead batteries versus charged ones. I also try to keep batteries paired for life since they do have a limited number of charges. Pairing a new battery with an old one can lead to issues with rechargeables. As a result, I usually mark the batteries on the end cap, identifying the item they power and the date they went in service. I have found a nice 15-minute quick charger that will also put a maintenance charge on the batteries, if you forget and leave them in the charger. It will charge one, two, three or four AA or AAA batteries. It is powered by a heavy duty 12V wall wart. The charger states it takes a power source from 11V to 16V, so you can also power it from your car battery:

Energizer AA 15-Minute Charger w/4 NiMh AA Batteries

I chose to go this route rather than a dedicated solar charger to give me more flexibility. I have several other items, like an Icom IC-T90A, that use 12-16V to charge as well. It then becomes a simple matter to use a generic solar charger with generic solar panels to charge all of my electronics. Currently I use a Tycon TP-SC24-10 12/24V 10A solar charge controller because it is what I had on hand. You will need a charge controller capable of at least 10A at 12V because that Energizer charger may be small, but it can really pull the juice when it’s in 15-minute charge mode.

With a setup like this, you can be semi-portable by using small solar panels. I use two in parallel that I picked up at a garage sale. They measure 18” x 18”. As an alternative, you can be completely portable by using a flexible roll-up solar panel.

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