Is your Zumo 550 becoming senile? Forgetting where it was and what it was doing last time you used it? Well, you may be surprised to find that there is an internal battery in the 400/500 Zumo series, in addition to the large external main battery. The removable main battery provides power only for the operation of the receiver, but not the real time clock. The non-removable internal battery maintains device memory. The symptoms of failing internal battery are: Excessively long time to lock onto GPS satellites after power up. Loss of time-of-day. Powering up in wrong daytime/nighttime display mode. Reverting to XM-radio preview channel instead of last-used channel with the GXM30 sat radio puck. These GPS receivers are becoming old by now; it is likely that your Zumo is having this problem. Note: I believe that this post should pertain to the whole Zumo 400-450-500-550 series. I only performed the operation on my own 550 - open your device to confirm the location and type of the internal battery. You should be able to replace the internal battery if you have some elementary electronic tools and skills. I purchased the replacement battery from www.palmdr.com for just under $10; they also offer repair service if this is beyond your abilities. Here is the procedure. 1. Your problem: the Zumo 400, 450, 500 or 550 receiver loses its memory of last-used state, including time-of-day. This causes very long GPS resync times. 2. Remove the external "backpack" battery. Depending on model and date of production, you may have to unscrew a T-10 Torx security, an Allen-head or a Philips-head screw. 3. You may be able to defeat the Torx security by jamming a small flat screwdriver into the fastener and using pliers to turn it. 4. Pop off the top cover ('cap’) by twisting a coin or flat screwdriver in the slot; remove the T-6 screws from the hinge of the bottom cover. 5. Unscrew the 4 fasteners from back cover of the receiver - most likely T-6, though I have seen Philips-head as well. Open the receiver. Gently! There are some wires in the way. Do not disconnect anything. 6. The battery is under this shield. Remove it. 7. Now de-solder the internal battery. 8. These are the solder pads, once the battery is removed. Make sure to correctly place the replacement battery on the pads, avoiding short-circuiting it or applying reverse polarity to the circuit. Dab a little silicon caulk or RTV onto the battery after soldering, to glue it to the circuit board, to prevent vibration from ripping it off the pads. From now on, follow the process in reverse to reassemble the receiver. Good luck!