Taijuan Walker was a gift to the Mets in the season’s first half, but what happens when the batteries start dying and new ones can’t be found?

Regardless of what the Mets might add to their rotation before Friday’s 4 p.m. trade deadline, they need a better version of Walker than seen over the last two weeks.

On Thursday he continued his post-All Star Game slide, allowing at least five earned runs for a third straight performance, in the Mets’ 6-3 loss to the Braves at Citi Field.

The Mets lost three of five games in the series and missed an opportunity to weaken a division foe’s chances of winning the NL East. The Braves trail the first-place Mets by four games, with the Phillies also very much alive in the race.

After surviving the previous night, with late-inning heroics from Brandon Drury, Jeurys Familia and Michael Conforto, among others in a 2-1 victory, the Mets were flat for the series finale, with Walker the most conspicuous.

Overall, he surrendered five earned runs on six hits with seven strikeouts and two walks over five innings. The right-hander was stung by two homers, giving him five allowed over his last two starts. Since representing the Mets in the All-Star Game, Walker has pitched to a 15.43 ERA in three starts.

“For me it’s been two things,” Walker said. “First, the long ball has been killing me and second is my pitch selection. The two [home run] balls I threw today, I’m just not trusting my stuff and when you do that you throw a pitch without conviction and there is nothing behind it.”

Austin Riley continued his torment of the Mets with a two-run homer in the fourth that gave the Braves a 2-1 lead. The blast was Riley’s fourth in three games and seventh overall against the Mets this season. Before the inning was complete, Abraham Almonte also homered.

Walker pitched to weaker contact in the fifth, allowing four singles that extended the Braves’ lead to 5-1. After Joc Pederson hit a roller through the second-base hole, Ozzie Albies delivered a bloop single in front of Brandon Nimmo for a run. Riley delivered an RBI single later in the inning to extend the lead.

“I think [Walker] pitched better than the previous two outings,” manager Luis Rojas said. “This was similar to the Taijuan we have seen for the most part this season. I think the fastball carry was there. For me that was the only concern, not seeing in the last game his four-seam [fastball] carrying. It was carrying today and he had his share of swings and misses with that pitch.”

Pete Alonso launched a mammoth two-run homer in the fifth that reached the top deck in left field and pulled the Mets’ within 5-3. The homer was Alonso’s 12th since June 28, the most in the NL during that stretch.

Dominic Smith hit a shot off the right-field fence at 104.7 mph that went for an RBI single in the third — he was out trying to reach second — that gave the Mets a 1-0 lead. It came after Almonte misplayed Brandon Nimmo’s drive to left field into a leadoff double.

With the trade deadline looming, Alonso was asked in what areas the Mets could use an infusion.

“The deadline is [Friday]?” Alonso said. “I don’t know, that is a good question.”

Then he added: “Getting an arm or getting a bat is great, but I think the No. 1 thing is for everybody to be healthy. If everybody gets back and healthy and we’re firing on all cylinders, that’s going to be just as big if not bigger than getting a trade, because we have got Jake [deGrom], Noah [Syndergaard] and Francisco Lindor that are on the shelf right now.

“Those are three superstars that aren’t playing right now because they are hurt and once we get them back it’s going to be scary. It’s going to be scary once everything in our pitching staff and lineup kind of lines up.”