Can I charge batteries & use load at the same time?

Hi. I'm building a portable music amp / speaker + power supply for camping. I have a UB1250 (12v, 5Ah, SLA) battery that will power a TDA7297 15w class D amp. It will also have a cigarette lighter output for powering small 12v, low power devices. 99% of the time the 12v socket will have a USB insert, supplying 5 volts to USB devices: a Bluetooth audio receiver for wireless operation, and for charging a phone in a pinch.

The battery is going to be sealed inside a container that has an power input socket which connects to the battery terminals. I have an external battery charger that plugs into the socket. My question is, will it be safe to turn on power to the amplifier / 12v socket while the battery is charging? I know the answer likely requires more information than I've provided thus far, so I am going to link directly to the items with specifications below... or just ask and I will find the information.

Battery: https://www.ebay.com/itm/380540510445?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Charger: **broken link removed**
Amplifier: **broken link removed**
USB Insert: **broken link removed**

Thank you for your time and advice!
-Scott

Operating the devices while charging the battery is similar to the situation in a car where the battery voltage is hold most of the time fully charged at 14.4 volt by the alternator and shouldn't be a problem.

The other question, not directly related to your question, is if the charger can still supply a net charging current to the batterly when the load is on.

I'd say no. The charger looks like is going full out to charge the battery, and with a peak current draw of 2A for the amp, a [say] 0.5A [max] draw for the USB the charger doesn't have enough capacity.

Ok, thanks so much for the replies guys. It's np... i'll just make sure not to use the amp while charging. I appreciate your advice!