I stumbled across this thread while looking for the solution to the same problem (dead rechargeable battery in a TDS 512K RAM Card). Unfortunately, the link to the charging procedure at tdsway was dead. After a little sluthing, I managed to find an old cached copy on the wayback machine. Here is the procedure in case anyone else is also looking for the instructions in the future and comes across this ancient thread:
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Maintaining data integrity on the 48GX
The 48GX is a reliable platform for collecting and storing your survey data. However, data loss can occur under some circumstances. Following the recommendations outlined in this document will help prevent the possibility of data loss and minimize the negative impact should data loss occur.
Download the data from the RAM card daily. Download to a laptop, or external storage device. In a worst-case scenario, the most you should ever lose is one day’s work.
Keep RAM Card 0 battery charged. The older cards had a replaceable battery that could be replaced once a year to keep a full current running through the card. These cards are no longer available and have been replaced by RAM cards that have a non-replaceable battery that must be charged in the 48GX to keep a full current running through the storage media. The 48GX must be turned on for the charging process to work. If your 48 is not used regularly, your RAM card will have insufficient power to maintain data integrity. This is the main cause of data loss. It only takes approximately 30 days of inactivity for a fully-charged RAM card to lose data.
The following procedure can be used to set an alarm to wake the 48GX up to keep the RAM card charged, or just prior to use if the card has been inactive for some time. This procedure takes at least 24 hours to charge a card for use.
Install new AAA batteries in the 48.
Hit right shift, then "4". This will bring up the 'Browse Alarm...' options box.
Select 'Set Alarm..., and confirm that the time and date of the alarm is set in advance of the current time, since the default value for the time field is the currently set time on the 48.
Toggle down to the 'REPEAT' section, which will display ‘NONE’, and choose 'Edit' from the soft key menu
At the arrow prompt, enter "299". The next prompt will be for the unit of time. Select ‘ Second’ from the CHOOSE menu.
To edit the alarm, select 'Browse Alarm...' from the main menu, then ‘Edit’ the specific alarm. To delete the alarm after it has served its purpose, highlight the alarm, then select PURG from the soft key menu.
Keep RAM Card clear of electro-magnetic fields. The RAM card is susceptible to electro-magnetic fields i.e. magnetic prism bases, high power lines, etc.
Protect the RAM Card from the environment. This primarily refers to dust and moisture but can also include extreme temperatures.
Keep job point numbers and point gaps schemes in control. It is possible to overflow a RAM card under some circumstances, such as by setting your first point as point 1 and the next point to 10,000 or some other large number. Since the 48GX can only store data in sequential format, the 48 will attempt to allocate 10,000 memory storage blocks to hold 10,000 points and thus lock a card out of free memory. A card with this problem generally cannot be recovered. Large point gaps can also cause problems for file transfer as well.