In short, no. To understand the difference between the Bosch 10.8V and 12V lithium-ion batteries is to understand how the industry got the voltage naming convention in the first place.

How did the industry arrive at these weird numbers?

A lithium-ion battery pack is usually made up of one or more cylindrical lithium-ion cell, in our case, a 18650, which has a nominal voltage of 3.6V. When fully-charged, the 18650 cell yields 4.2V. The power tool industry would then name most lithium-ion tool 3.6V, 7.2V, 10.8V and so forth.

Getting from 3.6V to 18V.

If you put two in series, 3.6V x 2, 2-series or "2S", you get a 7.2V.
Add one more in series, and you get a 3-series, 10.8V or "3S" (3.6V x 3). This style of naming convention more common in the hobbyist remote control (RC) industry than in the power tool industry. After a 3-series (3S) 10.8V, it's usually a jump to a 4-series (4S) 14.4V and after that, a 5-series (5S) 18V which is currently what the whole industry is focusing their attention on.

You will also note that with more batteries in series, you get higher amp rating (usually in amp/hour) which also translates to greater torque output from the power tool. A 3S 10.8V typically outputs under 50Nm of torque while a 5S can easily output well over 200Nm of torque.

Would the real 12V battery please stand up?

In Bosch's case, the GBA battery pack gets its name from the 10.8V battery pack in 3-series. If you look at the shape of the battery pack, it's obvious that only three 18650 cells would fit. Technically the 10.8V is the nominal charge of the 3S lithium pack (i.e., 3.6V x 3 = 10.8V) while a fully charged 10.8V would register 12.4V (i.e., 4.2V x 3 = 12.4V).

So what Bosch has done is to use the fully-charged voltage as part of the labeling instead of the nominal voltage the whole industry has adopted. This isn't unique to Bosch only as DeWalt too has been using a similar marketing tactic for their 18V and 20V lithium-ion battery packs. After all, the bigger the voltage number must also mean more power right?

Bosch 10.8V measured!

Here's a well-used Bosch 10.8V battery showing a 12.21V output (almost fully-charged) measured with our trusty UNI-T UT33C multimeter.

So for existing owners looking for replacement batteries for their Bosch 10.8V power tools, rest assured that these 'new' Bosch "12V" lithium-ion would work perfectly. We do recommend you grab the 2x GBA 12V 1.5Ah Starter Kit with the GAL 1230 CV charger instead.

Hope that helps clear out any confusion you may have with the 10.8V and "12V" Bosch lithium-ion tools and batteries!