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Motorola Talkabout T800 battery charger mod - charge AA NiMH batteries in radio

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n1das

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I wanted to share an easy mod for the Motorola Talkabout T800 and related Talkabout models to enable charging AA NiMH batteries in the radio instead of using the stock 1300 mAh NiMH pack. Using 2300 mAh or 2500 mAh NiMH AA batteries roughly doubles the operating time on a charge. The mod disables detection of AA Alkaline batteries so the battery charger is always enabled and can charge AA NiMH batteries. The mod is VERY simple: Open radio, clip one wire to the battery tray, and reassemble radio.

The Motorola Talkabouts detect the battery type by looking for a voltage present at one of the terminals between two AA cells in the string of 3 AAs to determine what batteries are being used. The stock 1300 mAh NiMH pack has 2 terminals, one at each end and doesn't contact the middle terminals in the tray so no voltage is detected there. When AA Alkaline or AA NiMH batteries are used, a voltage is present at the middle terminals and the battery charger is disabled. The purpose of detecting the battery type is to ensure the battery charger is disabled when AA Alkaline batteries are used. When the radio detects AA batteries are being used, it may also set the operating voltage range for Alkaline batteries instead of NiMH batteries but this is unconfirmed. It doesn't matter in this case because disabling detection of AA batteries so the charger will operate sets the battery type to NiMH, which is what we want.

To open the radio, remove 7 small Phillips head screws. You'll need a small precision screwdriver for this. CAREFULLY lift the battery tray out of the radio, taking note of the LED & vibrate motor cable at the top and the battery tray cable at the bottom.
Exhibit_9G_Exploded_View.png

Cut the YELLOW wire to the battery tray as shown below. This wire connects to one of the middle terminals between 2 AA cells in the string of 3 AAs in the battery tray. This disables detection of the battery type. The battery charger will always be enabled for charging AA NiMH batteries. Charging the stock 1300 mAh NiMH pack is unchanged.
Talkabout_T800_internal.jpgTalkabout_T800_internal_batt_charger_mod.png

The last step is to carefully reassemble the radio. Note there is an O-ring gasket around the battery tray for a weatherproof seal. Make sure the O-ring gasket is seated correctly during reassembly. When I did the mod, the gasket stuck to the battery tray when I first opened the radio and then it fell out. I found it easiest to install the gasket in the groove in the case of the radio instead of in the mating groove around the edge of the battery tray.

A few things to note:
  • This mod is completely reversible if desired by simply reconnecting the yellow wire that was cut to the middle terminal on the battery tray.
  • Be careful to avoid charging AA Alkaline batteries in the radio by accident since the battery charger is always enabled regardless of battery type.
  • Charging time for a full charge with 2300 mAh or 2500 mAh NiMH batteries will be roughly double the charging time required for a full charge with the stock 1300 mAh NiMH pack. The time for a full charge with 2300 mAh or 2500 mAh NiMH batteries will be around 30 hours. It's not a big deal if the radio tends to be left connected to the charger all the time when not in use. The benefits are the operating time on a charge is approximately double that of the stock 1300 mAh NiMH pack.
  • Charging with the stock 1300 mAh NiMH battery pack is unaffected.

I found the Motorola Talkabout T800 already has good battery life on a charge with the stock 1300 mAh NiMH pack when used according to a 5/5/90 duty cycle. It seems to have excellent standby time when not scanning and not hearing any activity on a channel.

I'm in the middle of testing battery life on a charge with 2300 mAh AA NiMH batteries so it will be a while before I have some numbers to report.
 
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n1das

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Battery test: 2 TalkAbout T800 radios, both in scan mode w/CTCSS/DCS set so all they do is scan. Scanning turns all battery save features OFF and consumes more battery power compared to being set on a single channel and standing by. Both radios were set on scan mode starting with a full charge and left powered on and scanning until the battery was dead.

T800 w/stock 1300mAh NiMH battery pack: 13 hours.
T800 w/2300mAh AA NiMH batteries: 26 hours.

Now charging the T800 w/AA NiMH cells in the radio and using the drop in charger accessory.
 
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n1das

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Battery test: 2 TalkAbout T800 radios, both in scan mode w/CTCSS/DCS set so all they do is scan. Scanning turns all battery save features OFF and consumes more battery power compared to being set on a single channel and standing by. Both radios were set on scan mode starting with a full charge and left powered on and scanning until the battery was dead.

T800 w/stock 1300mAh NiMH battery pack: 13 hours.
T800 w/2300mAh AA NiMH batteries: 26 hours.

Now charging the T800 w/AA NiMH cells in the radio and using the drop in charger accessory.
EDIT: Both radios were set on scan mode starting with a full charge and left powered on and scanning until the radio shuts itself off due to a low battery condition. The batteries in each radio are not totally dead, just drained until the radio automatically shuts off all by itself.

The T800's beautiful blue OLED display remains ON while the T800 is in scan mode. I absolutely LOVE the display on the T800. It's the best of any FRS bubble pack and reminds me of some MOTOTRBO radios where the LED display shows through the case plastic. The display draws some battery power to remain on. I am finding the standby time when the radio is set on a channel and not scanning or doing anything else is excellent, even with the stock 1300mAh NiMH pack. The display automatically turns off after a few seconds of inactivity when not scanning or receiving or transmitting. Pressing buttons on the radio wakes up the display but turns off again after several seconds of inactivity. It takes around 2 days to drain the stock 1300mAh pack when the radio is just powered on and standing by on a channel. The standby time will be much longer with 2300 mAh or 2500 mAh NiMH batteries.
 

n1das

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Out of curiosity why not un solder it and remove it from the pin housing
You could do that but it's more work. It was the fastest and easiest to just clip the wire and easy to reverse the mod if desired. I left the end of the wire blunt-cut, i.e., just snipped it and tucked the loose end out of the way. It won't move anywhere given that it's twisted with the other two wires. When I do the same mod to my other T800 Talkabouts, I will snip the yellow wire at both ends, close to the battery terminal and close to the connector pin housing. Less risk of shorting to anything else that way. I'm not going to try to extract the pin from connector housing.
 
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