There are two possible reasons for this to happen:
1) The "new" battery is not new or is a fake battery, which does not behave as the original battery.
2) The meter needs to know that the battery has been replaced and needs to carry out a measurement of the battery, in order to evaluate the charging/discharging curve, so that it can charge the battery correctly and then show the corect capacity percentage.
Most field meter use batteries, which are really a battery pack composed of a set of 18650 Lithium battery cells. These are combined in series and in parallel to reach the desired voltage (V) and capacity (mA). You can have your old battery pack rebuilt by professionals, but this is not cheap, as good 18650 cells easily cost around 5 Euro in Europe and if you need for example a 12V 4000mA pack, then you need to combine 3x 18650 in series to reach 12V and 2x three of them to get around 4000mA: this means you need 12 cells. At 5 Euro each you are looking at 60 Euro! Plus the work to assemble the new pack using the existing carging circuit from the old cell you get quickly at 80-100 Euro.
Never try to build those packs yourself, as Lithium cells are dangerous and can explode (mostly in your face).
I don't know how to calibrate the new battery on a Horizon meter. Rover Instruments/Prime Digital and their OEM's have a special function to do that.
Ultimately you can try a few charge/discharge cycles. But I doubt this will help much.
Regards,
Vitor
