Retevis RT3 Charger modification

I recently bought a Retevis RT3 radio and assembled a DVMega hotspot to dabble in DMR radio.  While the RT3 seems to be a decent handset for the money the charger leaves a lot to be desired.  Unmodified the charger will not cut out until the battery reaches 8.6 volts which is well above the 8.4 volts of a full battery.  This must be a hazard or at best will ruin the battery quickly.  However it is easily rectified as described here RT3 Charger Mod.  I didn’t have suitable smd resistors but I still used regular wire resistors to make up 390 ohms.  However even after the mod another shortcoming was evident – the charge rate is around 150ma so takes overnight to charge.  I purchased an 8.4v charger from the orient for less than 5 euros including delivery: 8.4v Intelligent Charger

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The “intelligent” 8.4v charger.

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Before modification (the 2 wires on the left were the result of the previous modification to reduce the charger voltage).

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After modification

The modification is very simple – the charging circuit in the dock needs to be bypassed by cutting the positive track near the dc jack.  Then connect the dc directly to the charging terminals.  The red wire on the right of the picture (negative –  just needs to be relocated to the dc jack (note the track cut just to the right of this).  The yellow wire is the positive.  The positive terminal was hard wired to the underside of the circuit board – this needs to be cut.  Now reassemble.  Note that the charging led no longer functions but the new charger has a status led on it so that’s not a problem.  A full charge (to 8.4v) now takes just 2 hours and 40 mins – respectable.  That’s two birds with one stone hi.

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