No more changing batteries! Olivers Technology is now offering to upgrade your REX 6000 so that it can charge in the cradle. This company will install rechargable batteries and a charging circuit directly into the REX so that it will charge when sitting in the cradle. It takes 14 hours to fully charge, but you shouldn't have to do this every day. The regular CR2016 batteries deliver about 90mAh and the rechargables used deliver about 45mAh. Given these numbers, you will have to fully charge the REX at most twice as many times as you had to replace the batteries.
The batteries in your REX 6000 PDA can last many months, or only a week. This depends on how much you use the device, and how hard you work it. If you only check your calendar and task list a few times a day, the batteries will last a long time. I really put my little PDA to work, so I usually get less than a month out of a set.
There have been some reports that different units have different power demands. Some units seem to draw more power than others. One unit may last for months while another may only last for weeks under the same usage conditions. (I think I own the latter.) What manufacturing variation in the hardware is responsible for this effect is currently unknown.
The REX 6000 uses two CR-2016 lithium button batteries. These are the kind that can last many years in a watch. Unfortunately, the PDA take up a lot more power than a little watch. At this time, there is not much we can do except conserve power, and buy batteries.
These are 3-volt batteries. The REX 6000 reports that they are low at around 2.86 volts, and gives you an warning soon after at around 2.82 volts. This is information based upon measurements taken off of the batteries in my REX (not under any load). The first measurement was taken when the indicator first displayed a half battery. The second was when it told me outright to replace the batteries.
There are different battery technologies. "CR" is a carbon-polymer formula that packs a lot of power. "LM" stands for Lithium-Manganese, which is newer and holds even more power. Both types are usually sold under "CR2016" to avoid confusion.
It seems that the major factor in power consumption is writing to the Flash memory. If you perform a lot of data entry and edits on the REX itself, then the unit must perform a write operation to this memory, which takes up a lot of juice. If you do this often, then your battery life will suffer. I've been playing with new Extra Applications recently, and was surprised to see how long this set of batteries was lasting. I also haven't been doing much editing and data entry lately. It seems that CPU activity does not have as much effect on battery life as do data changes.
When docked, the REX draws its power from the dock, not the batteries. This goes for the USB, serial, and PCMCIA docking solutions. Therefore, it is best to do most of your data entry in your PIM on your PC when possible. Uploading files, synchronizing, and optimizing memory will not drain your batteries. The REX will not sync without the batteries in place, however. It seems that the batteries always power some low-drain circuit that is essential to synchronization.
battery saving tips
Below is a battery chart with the manufacturer's specifications for the power contained within their CR2016 batteries. The number is in milli-amp-hours (mAh), which is the amount of current the battery can sustain over time. For example, a 90 mAh battery can theoretically last 90 hours with a 1 milliamp constant drain, or one hour with a 90 milliamp constant drain. Look at it this way: Measuring electric capacity in mAh for a battery is like measuring water capacity in liters for a bucket. The higher the number, the better. The best numbers here are marked in bold.
where to buy
These batteries can be quite expensive. Some places charge $3.00 or more for one battery. If you look around, you can usually find a good deal. I found that The Home Depot sells Duracells for $1.99 each. Also, Radio Shack sells a box of 25 for $16.75 with free shipping (67 cents a battery). You can also order over the phone at 1-800-THE-SHACK. ASpencer sells a 25-pack of lithium-manganese CR2016 for $15. There are mail-order warehouses that will sell them to you at wholesale prices. For example, one place sells them for $0.55 but you must buy a box of 50!
Rechargable Lithium Manganese and Vanadium Pentoxide Lithium button cells have recently been developed. So far these are only for use by manufacturers to permanently install into their products. Getting hold of these (as well as a charger) through retail channels is difficult, if not impossible. I'm looking for more information, and will post it as I find it. Take a look at Panasonic's lithium manganese (LM) and vanadium pentoxide (VL) products. Panasonic has CR2020-type cells, which are 0.4 millimeters thicker than a CR2016. They should fit.
Chargers for these batteries are very simple. Panasonic recommends a fixed-voltage charger for best performance. Trickle-charging, pulse charging, and fast charging are no-no's. Overvoltage will destroy the battery, while undervoltage will cause the battery not to take a full charge. Voltage must remain between 2.8 and 3.2 volts for lithium manganese batteries and between 3.2 and 3.6 volts for vanadium pentoxide batteries.
These batteries can be ordered in bulk on-line from DigiKey. Vanadium pentoxide batteries are really expensive at $4.75 each. Being rechargable, this is a bargain in the long run. Panasonic says that DigiKey also sells the LM2020, but I haven't found it. Note that these batteries come with tabs which must be removed. This is easier said than done, since damaging the battery can expose you to dangerous chemicals. Panasonic says that they are also available without these tabs. Here is Panasonic's list of distributors.
Note that not all lithium manganese batteries are rechargable. Do not try to recharge any button batteries that are not made to recharge! Explosive gas will build up inside the battery, and will cause a lot of damage or injury.
Other, bigger batteries will fit into the battery slots, but you do so at your own risk. The thicker CR2020 (2.0 mm) and CR2025 (2.5 mm) button cells cause the case to bulge a little bit, and place extra stress on the portion of the display that rests over the batteries.
You can also extend battery life by running the PDA in the cradle. To do this, you will need to install the DockPatch patch into your firmware. This patch allows you to either choose to sync or use your REX when you place it in the cradle. Since the unit draws power from the cradle when it is docked, it won't drain the batteries.
There is also the possibility of building a powered case using a PCMCIA slot, four AAAA batteries, a simple, low-power voltage regulation circuit, and a case big enough to hold the whole thing. See the Hardware Hacks section of this web site if you feel adventurous enough.
For even more information on batteries, see the "Battery Vendors" section on the REX 6000 Help Page.