Salter Brecknell S122 - Manual (Page 14)

When this symbol flashes, you should either replace the ‘D’ cell
batteries or recharge the internal battery.
Do not leave discharged batteries in the scale, as they may leak
and cause serious damage. Do not store the machine with 'D' cell
batteries in the battery compartment.
Recharging the internal battery
While the machine is connected to the AC power supply and
internal battery is being recharged, the power supply light will turn
red, yellow, and then green.
To maintain the rechargeable battery in good condition, it should be
kept fully charged wherever possible. If the battery is to be stored,
the rechargeable battery should be fully charged before storage
and then recharged at 3 month intervals.
Disposing of the scale.
The scale contains a lead-acid battery. When disposing of the
machine, you should take it to an appropriate recycling facility.