How does it work? Direct borohydride fuel cells are a type of alkaline fuel cell. They don’t use expensive catalysts and produce Borax (NaBO2) and some water as byproducts. The borohydride reactions are noted directly below:

At the cathode: 2O2 + 4H2O + 8e- => 8OH-
At the anode: NaBH4 + 8OH- => NaBO2 + 6H2O + 8e-

Medis says it uses a mix of alcohol and sodium borohydride. The electrolyte is potassium Hydroxide, KOH. Combined with their proprietary anode and cathode, this accounts for the higher power density I saw in their cell.

I measured an initial voltage output with a VOM (volt ohmmeter); on a standard DC volt scale, the voltage initially measured 5.26 V and slowly declined, not surprising, since the VOM would draw current across its internal resistance. On the VOM battery scale, the voltage measured a steady 5.42 V, which was just about what was claimed.

Use And Tests

Medis recommends using the unit for no more than two to three hours at a time to extract maximum life from the activated fuel cell. One downside is that the unit uses a proprietary connector, so an adapter is required. A set of cell phone and mini USB adapters may be purchased separately, or in a combined kit. One of my kits arrived equipped for a Treo, a Nokia and a Blackberry. I was able to use the Nokia adapter to recharge a borrowed Nokia 770 Internet tablet. The LED on the Medis connector glowed faintly green when plugged into the fuel cell, then when recharging, the 770 glowed brightly?

Charging the Nokia 770 with the Medis fuel cell. If you look carefully, you can see the charging icon on the Nokia 770. The LED glows faintly green on the Medis cord, then brightly.

An Alternative That Uses Lithium Batteries

Another manufacturer, BoxWave sells a mobile phone recharging device, called the VersaCharger Pro that uses two AA lithium batteries, each of which offers 1.3 charges. Considering that up to 10 charges are possible from the fuel cell and given the lithium batteries cost, this fuel cell would be marginally less expensive. Though lithium batteries do have a longer shelf life than the Medis charger, not many users stock several sets of lithium batteries for a rainy day. Obviously, any large, spare rechargeable battery used to power a phone or MP3 player will be cheaper to use, but you have to remember to keep fully-charged batteries around. What do you do when you can’t charge the batteries because power is not available?

The next generation of the Medis fuel cell, already in prototype, will be about one third slimmer, and will be reusable; a cassette/cartridge system replaces the used electrolytes. Medis will accomplish this by using an embedded gel between the anode and cathode. Within the next two years, Medis states they will be able to increase the fuel cell density to 60 mW/cm2. That means we could recharge laptop batteries at 12 - 14V. This would be incredibly useful in all sorts of remote locations, and the fuel cell typically will be smaller than the laptop battery. Medis has even demonstrated a 700 W cell That uses their technology, though not in such a compact form factor.