source: http://www.cypres-usa.com/faltblau.htm Quote: Every time Cypres is switched on, it will calibrate to ground elevation by measuring the air pressure several times in a short period of time and taking the average value as the value for ground level. This is happening during the integrated self-test which also checks the battery, the entire internal electronics, etc. If this check is successful, Cypres will go into function - otherwise it will shut itself down. Endquote: source: English Cypress user manual Quote: Battery failure or low battery voltage will be detected by CYPRES. At the end of the self-test cycle, CYPRES will stop with an error display of 8999 or 8998 and will not assume operating mode. This indicates that the energy supply of the battery is no longer within operating limits. Replace the battery once the self test has stopped at 8998 or 8999 (voltage too low),after two years or after 500 jumps, whichever comes first. Endquote Definite internal problem, not just the battery. Low battery or battery failure will indicate on the LCD and show an error on the start up selftest. The two states are distinct - a battery can have a good voltage reading but low charge (like rechargable Ni-Cd's that run equipment fine and die very quickly at the end) or plenty of charge but degraded voltage (can be caused by corrosion or oxidation on the contacts). Either way it seems that you'll get it sorted fairly easily with SSK for no charge (no pun intended). Ya can't say fairer than that.